I'd suggest avoiding the brass screens. Have read here on FC they are not so good regarding off-gassing.
I saved this from reddit a while back, so take with grain of salt, but info looked pretty good...
This was from a Smoking Post, so warnings were related to Bic Lighter and flame temperatures... adjust accordingly to determine risk at vaping temps... Some good data and some... 
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here is a little, or a lot of information for digestion. those brass screens that are sold at corner stores or in head shops are composed of copper and zinc (brass is 60% copper and 40 % zinc). the steel ones they sell are either carbon steel (99% iron, 1% carbon) or stainless steel which is a more complicated mix of iron, carbon, chromium, nickel and/or manganese (many people are familiar with 18/10 stainless steel for cooking vessels such as pots and pans - this means 18% chromium, 10% nickel). you can also buy glass screen or titanium ones, but I have yet to see a quartz screen which seems to be the most resilient of them all. what does this all mean for pipe screens?
consider this:
brass screens (60% copper, 40% zinc)
yellow brass has a melting point of 1710 F
steel pipe screens are made up of carbon steel or stainless steel.
carbon steel has a melting point of 2600-2800 F stainless steel has a melting point of 2750 F
titanium pipe screens are made up of just titanium
titanium has a melting point of 3050 F
what this should mean to you?
those brass screens you buy or get for free from the local stores are the cheapest of them all. anyone who has used one knows they give off an almost metallic taste when roasting a bowl and if they are used long enough they will develop a hole right through the middle. where do you think that brass has gone? how much off-gassing happened as a result of the intense heat exposure.
is glass better?
borosilicate glass should not be subjected to heat greater than 932 F as a normal operating temperature as 950 C is when thermal stress can set in based on it's thermal properties - this greatly reduced the life of the glass. and once you reach 1508 F, the glass begins to soften and at 2285.6 F is the temperature a glass blower needs to work with borosilicate glass.
quartz seems to be the winner as it has a continuous operating temperature of 1832 degrees Fahrenheit, becomes strained at 2048F and has a softening point of 3061.4F - I do not know the melting point, but logically it would be an even greater number. this appears to be the most resilient glass and it also has a thermal expansion that is 15 times lower than soda-lime glass, whereas borosilicate only has one 3 times lower and is known to crack when exposed to rapid temperature changes - quartz has been said to be heated up to 2012 F and then immersed in cold water with no adverse effects. so quartz is definitely superior to boro glass, but it comes at a hefty price as it is inherently more difficult to work with.
If you can find a quartz screen for your pipe, you are looking at the safest and longest lasting glass pipe screen.
why do brass screens exist then as I see them everywhere?
my theory is simply this, combustion of cannabis or tobacco happens around 446 F and above while achieving a temperature range of 932 to a maximum of 1292 F while it combusts entirely and turns to ash.
in general, when you smoke a tobacco pipe, you light the top of the bowl and keep puffing while it continues to burn all the material - you don't hold the flame over it for long, just enough to get it to start to light - so when used in this way, it doesn't appear the brass screens are inherently harmful because they have melting points of 1710 F.
This is why I believe brass screens are readily available as they are often used in pipes where you put the lighter to it for a second or two while pulling and the bowl is lit - which again only reaches a maximum of 1292 F during the combustion process.
So if they are safe for pipe smoking, why not in the bowl of my bong or cannabis pipe?
the problem here is the difference in methods of smoking cannabis vs tobacco. when smoking cannabis and roasting a bowl or killing it off in the bong - what do you do? you hold you bic lighter and sort of evenly distribute the heat throughout as you are pulling and sometimes people just hold it there until the bowl is pooched - this is the problem.
How hot is the flame of my Bic Lighter?
Bic Lighters have a maximum flame temperature of 3590.6 F. when you hold that lighter there for more than a second, the heat is going to be making its way down to the screen and that is more than enough heat to melt both the brass and stainless steel screens. I suggest this is why the holes form in the center of the screen because the heat is directly right there as you are pulling through you piece - so the most intense part of it will be hitting the bottom of the bowl and providing a significant amount of heat and possibly enough to start melting them - or over time slowly. one thing is for sure, that hole that appears in the screen is caused by it melting.
even the titanium screens have a melting point of 3050 F so it doesn't seem like you really win either way. It wouldn't appear than titanium is far superior to stainless steel as it only has a 300 F higher melting point and you shouldn't be exposing them to that much heat.
--Also, when people say to torch your screens until they are red hot and everything burns off is just a bad idea, because even a bic lighter generates easily enough heat to melt the brass and theoretically enough to melt the stainless or titanium.
It appears you can't win
However, almost just as important as all the other info - thermal conductivity is a big factor as this can determine the ability to actually generate those temperatures - as some dissipate the heat quicker than others, thus increasing the amount of heat that needs to be applied to actually reach that maximum temperature. so holding your bic lighter to titanium isn't going to instantly melt it, it prob won't ever as it doesn't generate enough BTUs to effectively transfer all that heat to the material - but maybe someone with more experience here can chime in - I don't have a great explanation for it. However, this also suggests that brief application of a lighter flame to even the brass won't be immediately detrimental, but going with something that has a melting point 1000 F higher seems to be playing it safe - also I can't get over those holes that get burnt right through the screens!
So if my Bic lighter can theoretically melt any screen median, what then?
the brass screens easily melt (3590.6F flame from your BIC to brass which melts at 1710 F ) and also is a potential threat to stainless steel and titanium which have melting points of 2750F for Stainless Steel and 3050 F for titanium, what options do I have left? Glass? Well we learned than borosilicate glass experiences thermal shock at 950 and softens at 1508 F whereas quartz doesn't experience shock until 2048 or soften until 3061.4. Importantly, even though it seems nothing is safe, the less you hold the flame to the material, the less exposure it receives and is less likely to heat to the critical point - also thermal conductivity and resistance are important facts, but requires physics to explain however it suggests that the BIC lighter, although reaches close to 3600F is not actually powerful enough to transfer enough energy to detrimentally affect these materials.
My Advice?
go with the material with the highest heat melting point, it is better to be safe than sorry as on paper, the brass and borosilicate screens are exposed to volatile temperatures in typical smoking methodology. Quartz and Titanium seem to have the highest heat resistance, this suggesting they aren't going to be a detrimentally affected as their counterparts with lower melting points.
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