I'll third the rx200, as long as you're ok with it being a bit bulky that is. if you want a sleeker mod then there's lots of options but as far as performance capabilities and price, nothing beats that currently. And, while you may not use it right now if in the future you want to go to 200w, well that's capable of it, so it's basically a "future proof" mod. For sleeker options, there are things like the VTC mini or even the Mini volt, but they won't live with you if you get the inclination to push further, but they're nice and small.
Tank wise, well first of all everything f1r3b1rd said is spot on, people have different preferences and there's honestly a ridiculous amount of options out there to suit different needs. Do you prefer the clouds for the overall experience, or do you want the full flavor? Do you like it warm or cool? Are you interested in making coils and wicking it yourself? Do you MTL (mouth to lung, suck it into your mouth then stop and inhale that) or direct to lung (just breath it in, abbreviated as DL)?
For premade coils with DL style the kings are The Crown and the TFV4 with the Crown being a bit more cost effective with cheaper coilheads and the TFV4 having a larger variety and a bit more powerful coil options. Both solid, though both you'll want something capable of 150w most likely (each have options that are solid under 100w but the price point difference between 100w and 150w is not much and worth investing if you want to push it further).
For rebuildable options the Griffin seems to stand tall among the rest, though I know a bunch are a fan of the Crius v3 and Billows v2. Personally I've fallen in love with the Haze Dripper tank which is easy to set up but doesn't travel well, just amazing flavor. And there is the Avocado with a similar and in some ways better design.
If you want MTL, for rebuildable the Goblin Mini is the current king of the hill though I know there is a version 2 coming out and there are a few new ones coming like the Balrog or even the TFV4 micro, not sure how those will turn out.
For non premade coils on MTL style the GS tank and Nautilus seem to stand strong, you can get the Triton Mini clapton coils for the Nautilus which I've read many enjoy. Then there's the Protank which I know some are a fan of.
If you want a lower power DL option there's the Kanger Subtanks and Aspire Triton/Atlantis which are hugely popular (basically the average setup, no matter what vape store you go to they'll have coilheads for these two tanks).
So as you can see there's kind of a stupid amount of options and your personal preference will determine what you like.
One thing I'd say is I'd advise getting a mod(battery) with replaceable batteries. It allows you to carry spares so you can charge while you vape, but not only that, all batteries have a lifespan, and with fixed batteries you'll end up throwing the mod away eventually where with replaceable batteries it'd be a long time before you have to do that as you can just buy new batteries (they last close to or over a year depending on treatment, though always buy quality, Samsung 25r and LG HG2 for longer duration and Sony VTC4 for higher power is what I'd recommend).
Anyways that's a lot to take in I'm sure, tell us more details about your goal and I'm sure you'll get some narrowed down results.