I briefly had a pico and am one of the few that wasn't too fond of it. With that said, tons of folks like them. I would recommend against getting the Melo III tank though, it's not very MTL (although it will accept some non-proprietary coils). I just found I wasn't getting great battery life out of it, although it is small, easy to use, and pretty reliable, it just wasn't my cup of tea.
I have both a Zenith and a Nautilus 2 and a Ego Mega one with the Ccells, which are all good vapes. If I had to rate them, it would be:
Ego one Mega V2 with not the original coil, but the Ccell 1.0 MTL coil, great flavor
Zenith: Nice MTL vape, very reliable, the 1.6 coil lasts forever. It is 4 ml in size but vapes like a smaller tank. The 1.6 coils have a break in period of about two tanks, after that the flavor is excellent. I'm glad I got this tank. It can be fairly cloudy for me (not exactly sure why) but give great flavor. I haven't tried the 0.8 coil yet, wanting to find out coil life on the 1.6 coil. Better flavor than the N2, but not the ego one mega.
N2 is a great little tank, it's easy to use, but the capacity is the smallest, and I'd probably rank it third for flavor.
With that said, I'd recommend a Kabuki clone from FT if you are willing to wait a bit. It takes the Nautilus coils but turns them into flavor machines. It is bottom fill, but a fairly easy bottom fill. I'd recommend a clone first over the original to see how you like it as originals are pricey (to me, they are also noticeably better) but it's worth the investment in a clone first to see if this tank is for you. Instead of the hassle of refilling every 1.7 mls (about what you get if you are filling correctly) you will get about 3 ml instead with the kabuki.
Finally, I recommend the Njoy Elf tank which also takes N2 coils and is very similar in design but fixes many of the N2 problems: A true 2 ml tank, topfill but easier topfill, better airflow and flavor, it kind of fixes many of the N2 problems.
I started with N2s, and they are great, but I am primarily using different MTL tanks now, and my husband is starting vaping with my N2s.
You actually have some decent options. If you are interested (even in the future) in trying sub0hm vaping, it might be worthwhile to get an inexpensive 2 battery mod as you will have great battery life and also the ability to "move up" in vaping should you so desire. I'd probably recommend that over the pico, unless you want an internal battery mod, which is possible to obtain with one of the older pico models.
Best of luck, indeed there is a lot to choose from!
Anna