I'd like to see the general consensus on who picks who for the first party. Who knows, maybe it'll influence my choices the next time I play.
Virtually every playthrough I've gone with Rheda. Her naming magic, I've found, is incredibly useful in almost every situation, being able to strengthen her party and weaken her enemies before engaging in melee combat, then making her a competent fighter with Swords, Warrior, Thief and Shield. She's extremely versatile and that's part why I love her so much, the other part being her characters story.
I've never touched Godric, primarily because the only offensive magic I really use is on Alaron, and I've found his Alchemy skill to be of little use after reaching Erromon, when Curing Potions become available for purchase.
To be honest I've only beaten the game once, but Rheda and Brenna stayed with me the entire game. I had to give up Abrecan at some point to get into Shamsuk's Tower, but afterwords I got him back, and finished the game with the original party. Something about the default party is sentimental to me.
The one time I kept Brenna was simply because I didn't want to level up someone else. Otherwise I would have booted her the second I got my Mace of Glory, and replaced her with Keelan. But Rheda and Abrecan are pretty much with me forever.