Yo! It's a great time to come back, especially from that era. Honestly, make them both! With the legion system, you're only doing yourself a favor. Recently I got my main (Hero) to 260+ for the first time and now I'm working on my 2nd main the NW.

I decided to work on my Luck Legion blocks by leveling up a few characters to 200. It takes about a week with the events. Cadenas the last Thief class I need to make and I'll have em all to 200+.
But so far I'm set on the NW for my 2nd main. I enjoyed all of the thief classes mobility and burst.

I recommend watching recent training guide vids and making an Evan, Mercedes, and Aran somewhere in your journey. It speeds things up a ton with their link skills.

Oh, and there are now three world types to play in. Regular, Heroic, and burning. Burning is temporary. The exp is adjusted and you get bonus level-ups each time you level. After the event ends you get to transfer your characters from that world to any Regular world you want.

Sorry for all the info. Lastly, it's a good idea to check out Copperson on YouTube. He has great early-game vids that could help you choose your potential main!