Checking up what more laid back class that easy to twink and alot of fun to level from 1-220+ and also strong doing AI stuff ?
Soldier, Fixer, Agent. I suggest Fixer. Read this:
https://www.aofroobs.com/viewtopic.php?f=9&t=3410
I also suggest going to RK5 where-- RIGHT NOW-- you can do daily missions (ELite, Regular, & AI…& every other week-- Freelancer missions), accrue victory points to spend on OFAB gear, and have access to the auction house. Or you can wait for a couple months for FC to enable all of that on RK2019.
Was looking into Soldier though seems alot of fun and agent (prob for pvp) not fan of fixers
I’d say agent is in a very good place right now.
And even in PvE, they deal way more damage than soldiers and fixers.
Very easy to level with FP MP in the beginning, weaving into doc at higher levels.
Sorry about the necro! 
I might be biased, but I’ll say fixer.
Fixer is the best class in the game if you are lazy and impatient like the majority of gamers
Agent is fun but it feels like cheating sometimes with how glaringly overpowered it is in pvp and managing false profession can also get kinda tedious
Soldier is great in groups but too one dimensional for efficient solo IMO