Which Rebel leader?

Ackbar was the first character I ever farmed, and I've never regretted it. With him as your lead, not only do you get a speed increase, but a tenacity increase as well. His leader ability lets you get around counter-attacks (assists do not count as attacks). His dispel is a must have for P1 of the Rancor raid and is becoming more important in arena with Anakin and EP running around. His main weakness is he hits like a toddler. But your other rebels should make up for that.

Wedge is nice, but you are in a for a very, very long gear grind. I also find him too slow as a leader for arena. If you already have Biggs, I'd say go for Wedge, but after you get either Ackbar or Lando. If you try to farm him first, I suspect you'll get discouraged.

Lando is a must for rebels, I think. Especially since they fixed his AI. Plus he is so good for the Scoundrel events.

You're off to a good start. HRS is amazing once you get him to higher gear levels. He was my MVP during the recent Empire event. His time manipulation combined with StHan's is a nice combo.