Atlantis v1 is still a favorite of mine, treated me well for so long, still works like a champ, no complaints about it at all. And, while I rant a bit in this, I will preface it with my opinion that at a 50w max, .5ohm coil on an Atlantis is probably as good as you can hope for. It's great, I loved it for a long time before I decided to step it up a bit. And without a new mod you won't be able to really get much better than that (don't use the .3ohm coils on your Atlantis, or do, but IMO the .5 was far more enjoyable at 50w max).
That said, I've moved to the TFv4, I think it's a nice logical step. It's prebuilt coils are more powerful, honestly too powerful (gigantic clouds, tons of juice, meaning tons of flavor). With that I think the prebuilt coils are honestly a bit too airy for my taste, not any more airy than my Atlantis, but the RBA decks, ohh those babies shine. I'm running a dual twisted 26g coil at .2ohm on the dual deck right now. Hitting it at 92watts. I get this nice thick delicious taste from it. It can be a bit finnicky, I had my first dump this morning when I thought I didn't need to replace the wick and tried to fill it to the brim. But, if you follow "the rules" it's honestly not been an issue. If you're looking at RBA stuff, well, this tank is a solid choice. Screw up a rebuilt, ohh well, toss in a prebuilt and keep vaping while you figure out your mistakes. I've been reading a lot, wanting to keep progressing in my builds, but I'm not really into the idea of dripping so I'm looking at RTAs. Well, the more I read the more I see this tank continuing to pop up in the discussion. Maybe there's something better out there for the RTA world, but as I see it right now, this tank is up there in that realm and up there as far as simple tanks with prebuilt coils go.
But, that's just the start of the TFv4. Really, the versatility is where it shines IMO. I'm a bit weird in that my preferences flow on a whim. Sometimes I want that big cloud. Sometimes I want that huge hit of flavor. Sometimes I want a nice long slow hit with a super thick but small cloud. I've found I can tweak my coil to my preference. The Quad coil on the TFv4 like I said earlier is a bit too airy for my taste, but massive cloud and even with the airiness there's a lot of flavor there just due to the amount of juice you're pulling in (run it at 110-140w). Then I have my Dual coil build, thicker vapor, equal taste, smaller cloud, more to my liking (run it at 85-100w). Then I have my Vertical single RBA builds which I run at about 65-80w, more airy, but less so than the quad but also less vapor, reminds me of the Atlantis, basically mimics it, again I like it when I feel like it, running .3-.8 ohm coils on it (my project trying to perfect this one so I rotate coils quite often). Then I have the single horizontal coil, which I've run all the way up to 1.4ohm. With this I can toss it on one of my sleeker mods and get a solid taste without the big "obnoxious" cloud, something I like when I'm going out and don't want to be "that guy", I can sit on it with a nice deep more MTL type hit and be satisfied.
Anyways, it's a nice tank if you're looking into rebuilding but want the option to forgo that if need be. You can buy the full kit for around $30 + shipping. The Dual RDA another ~$8. Building coils isn't too tough, a Coilmaster v3 does help (I'd opt for the v3 if you do go that route, or a different brand with that same longer rod), but isn't necessary. Solid screwdriver/drill bit will work just fine. The wicking is the tougher part as too much cotton means wicking issues, and not enough means leaking/draining.
As an addition to all this, I want to be fair and give some warning. I believe I mentioned it can be a bit finnicky on the RBAs, gotta learn to wick correctly. And, I don't know if I'd call it the best of anything. From what I read, not owning these, the Crown seems to be the favorite for a strait up Subohm tank with prebuilt coils. Goblin is a fan favorite for MTL users. And there's a couple different great RTA's out there. But, I feel like I get a ton of versatility out of what I have with the TFv4. A little bit of work and I can satisfy any urge for any different style I'm interested in at the time. And, that's why I think it's a great tank. So maybe not the best for what you're looking for, but for myself who is a fan of changing things up, it's perfect for me.
But, again, if you're looking to take a step up on your tank, you're likely going to need to take a step up on your mod as well.