I had both the seqonia, siaonara and DTv4. All with TI buckets. I prefer dabbing off TI.
The worst is the siaonara. The small bucket tends to splash and ride up more. More messy, and not as powerful.
The DT V4 and seqonia are petty equal. Seqonia is built like a tank, large bucket and very well built. Very easy to use and install new coils. I do wonder if HVT will go out of business due to the vape mail rules. They did stop shipping for a while.
Flavour is better with the DT v4 but it's not as easy to use or setup. There is a learning curve when replacing the buckets on the DT v4, and can be troublesome when not setup right. You get mod errors when a bucket is setup wrong and screws can become lose overtime. Once you have it installed good, best not to mess with it I find. A good install will last a long time if not messed with. Best to use a better screwdriver than the supplied one.
I think the DTv5 will sort out these problems. Personally I would wait for the v5.