For me I always look at how reduced the chamber is, the diameter of the air hole on the deck, whether the chamber has a bell curve to it. I am extremely picky about which juice I run in each tank because the properties change so much. I also tend to check if a tank has a full stainless option because I find the heat really helps with certain flavours, kind of like a pressure cooker. These are my opinions on most of my favourite RTA's.
Kayfun Lite V2 Plus. This will always be a favourite of mine because it still offers very good flavour and has an almost chewy quality to the vape which makes you want to really savour each inhale. Fabulous with custards, good with fruit but outclassed often with tobacco vapes. At least in terms of what I enjoy. Can get away with 70VG but tends to clog sometimes. Worth putting up with due to capacity.
Gus Mods Phenomenon Lite. Extremely reduced chamber and is outstanding to this day for juiciness when it comes to apple and other fruity vapes. Building is a touch fiddly due to limited space and filling is a chore. Good in general up to 70VG.
Rose V2. As mentioned by
@TrollDragon It is something of a pain in the neck to build and wick and has too many parts and little quirks which would likely put off most average vapers. But once you get it right it is fantastic for fruit and tobacco vapes.
Taifun GT III. Superb for custards and tobaccos. Excellent range of airflow options but needs separate reducer to be true MTL. Juice control can be a touch over sensitive at times and it is a large and to some quite ugly tank.
GP Heron 1.5. Outstanding for Manabush tobacco dessert juices which I adore since the creator designed his juices for this particular tank. Can be fiddly for newbies to wick. Not so good with high VG. But so easy to fill and the O-rings have never failed on this beauty.
Tilemahos V2 Plus. Outstanding for custards. Lot's of parts make it easy to lose stuff down the sink. Can do MTL and restricted DTL. Gets very hot which suits certain juices.
Ataman II. Only have the clone but vaping tobacco in this is the equivalent of smoking Russian cigarettes. Insane throat hit and excellent tobacco notes. Fairly decent with fruit but sucks with custard juices. Raised airflow post effectively prevents any leaking even if the chamber floods.
Squape RS. With the bottom deck this tank offers almost dripper quality flavour with fruits and drinks juices. Good airflow options and super simple to build, but annoying to fill.
Evl Reaper V3. Most recent purchase and does an outstanding job with just about every juice I vape in it. Certainly in my top 5 tanks. Very dense flavour and once more that chewy vape quality. A touch confusing due to reverse juice flow control and the separate airflow ring might annoy. No problems at all with high VG. Definitely try the clone!
Dvarw. Truly solid RTA, similar design philosophy to the Ataman II which makes sense since the original comes from Eastern Europe. Kind of the tank you want in a vape apocalypse. No moving parts. Great with fruits, good with tobacco and very good with custards. Get the one with oval wick holes and high VG is no issue.
EHPRO True MTL. Excellent budget RTA. Fill port kind of stiff and you need to get the wicking right but delivers on point flavour especially with tobacco and fruits. Only issue I have with it is the poor capacity even with the bubble tank.
Then of course there's the Kayfun Prime and the Kayfun Lite 2019 but I don't want to overwhelm with info.
