I can't say that either one holds any grand appeal to me.
The "Thread Starter" one may be occasionally useful, but so many threads here go off the OT fairly quickly and other users become the major focus of the thread. In those cases, the need to see the "Thread Starter", or even the importance of being the Thread Starter, is diluted. And perhaps it's the pessimist in me, but I'd see this as another incentive for some people to start threads just to be the "Thread Starter".
The bolded user name could potentially be useful to those without Avatars, so having that as an option could be nice. Personally, I wouldn't choose to use it.