Here’s what I did in your situation:
I decided to try new mastery with FG so created an Oathkeeper. It’s very, very flexible and easy to gear.
I levelled it to fifty-five or so as a single mastery. You could easily go higher. This allowed me to get a feel for all the skills it had to offer and what ones I’d like to build on. I also looked at what gear I had.
I went Warlord as it’s very powerful and not difficult to play. Got to 100, enjoyed Oathkeeper so much I went back and levelled a Paladin too!
Farmed a bit with these characters, next thing you know I’m making Oathkeeper + ‘X’ toons all over the place. Archon is especially good fun.
Hope this gives you some ideas, I honestly think Paladin and Warlord are very powerful in relation to the gear it takes to get them into Ultimate. Ofc you could also go Conjurer, another no-brainer.