Check out the following link to the post by CentiZen. Compares UD with E-nano.
Differences between HI and E-nano
The only thing to add to that is that the UD has a 3/8" diameter heater core and the Nano has a 10mm core. Smaller size heater core coupled with a more powerful unit makes for some huge hits.
When I had a Nano and UD I would always go do the Nano over UD when pairing with a water path, this is the only time I notice my Nano outperforming my UD. The Nano's gongs seem to be more refined than what UD offers and the smaller diameter makes it perform better with smaller loads. For dry sessions I reach for the UD and nylon stem every time, I enjoy the restriction of the ss tip.
They will get you to the same place, the Nano just does it a little better for me when using a water path.
If you're trying to quell your VAS then get a heavy hitter (Cloud, LSV, Sub, etc) for a completely different experience, if you're set on another log the E-Nano is a no brainer! Its an exceptional vape. Just keep in mind you'll have a similar experience with either log.