I'd like to add a type D where the beginning sucks, but the end is spectacular.
Well, let me think of some that would fit in each; it's a bit hard since many of the stuff is neither A nor B; going down my MAL with all anime I rated passing or better as well as what I gave them individually (gogo, unscientific tiering!)
A- Steins;Gate (9), Tiger and Bunny (9) , Shin Sekai Yori (9), Fate/Zero (9), Durarara (9), Kemono no Souja Erin (8), Inu X Boku SS (7), Hana Saku Iroha (6)
B- Clannad (9), Nana (9),True Tears (8) , Ano Hana (8), Mai Hime (8) , Yu Yu Hakusho (8), Kanon (8), Sola (7), Angel Beats! (7)
I would say it's much easier for me to approve of A since I usually look upon these better. Though I often end up talking about a successful show in B a lot, and often times it's because I'm really attached to a character's critical moments that cause momentary spikes that can be talked about. It can also be said that adequate type B shows seem to be seen favorably by me no matter how terrible the ending is, and damn a lot of these shows have shitty endings.