Thoughts for your secondary class don’t change it too much
Fighter (base or mutation warrior): Fighter is full BAB and gets weapon training for melee and eventually reflexes. Armor training or mutagen is a personal choice.
Ranger (guide): Full BAB, wisdom scaling, high reflex, team buffs. All solid.
Slayer. (Any): Skills, reflexes, BAB, and a flexible attack steroid.
Cavalier (Order of the star): You get more oomph out of your channels and full BAB
Inquisitor: There is a feat that adds inquisitor levels to cleric for channels. You also get a wis to initiative and some skills, more spells, judgements, and teamwork feats. I personally like sanctified slayer for talents and studied target over judgment but that is just me personally.