Personally, and this is of course only a personal opinion, if you like MTL
vaping there is still mileage in the original Nautilus Mini - and I say this with four years experience of one as my daily vape for most of that time.
Yes its bottom fill; is it difficult to use/fill - yes if you want it to be; no if you just accept that it's bottom fill and like anything else you'll get used to it ... and you may find the ritual of filling it quite relaxing just as a pipe smoker does filling his pipe and prepping it to smoke.
If you want simplicity and top fill then the choice is easy - go for a a Zenith or Zlide - they are both good; and again if you like MTL go for the 1.6 ohm coils and run them between 8 - 10 amps and they'll last for 6-8 weeks with clear juice.
All of these, at the 2 ml size, will work with/ fit on a Pico. If you travel a lot you may even want to look at an iStick 30w which you can plug in to charge anywhere including your car.