I picked someone who could handle Allies because I found that both Meri and Kyra had issues recruiting them. Between Lem and Seoni, I picked Seoni: only because I play Lem so much in the paper game. I have had no regrets, she is somewhat of a glass cannon at first, but with a little optimization I haven't had much of a problem keeping her alive. Having Father Z to give her right away was a huge benefit. If you do go with her, don't be afraid to chug potions early and often.
My second character pickup was Harsk. I felt I needed a weapon guy role and again, he's someone I haven't played with paper. He appeals to me so much more now. He is such a tank. WIth a crowbar, thieves tools and Elivish boots or spyglass and he can take down pretty much any location I send him to. The Only time he lets me down in combat is when I really need him to succeed. (henchmen, temp closes, etc) But I feel that's just bad luck more than his lower dex die. WIth a few + 1 weapons and i'm routinely rolling ( 1d8 + 1d10 or 2d8) + 6. and that bonus, usually, gets him there even on poor roles. His average rolls are so good, that I think i'm overestimating his ability when I really need a success, but I might just be being stingy with my blessings. Both his abilities are great. being able to do 1d4+1 to another character( like kyra or meri when neither of them have a weapon and you've just got to go for it) is huge.