As a gta02 owner, I am biased towards that.
As a lurker and osmocom supporter, the C1xx phones seem to have more of a future.
I also wonder which work will also help for future ports such as MTK.
The main issue with creating a usable phone though is getting people to use it. For gta02 you can simply get osmocombb included in SHR, QtMoko, Debian etc and voilĂ , instant users who care about software freedom. For C1xx you would need to create a user community from scratch and do a lot of work to reach the people who might be interested.
In both cases there is the whole legality/certification hurdle though.