Can't really say which one I prefer but the Sharingan has much more potential.
The Bayakugan isn't bad either though but from what i've seen so far, it is more limited than the Sharingan in terms of being useful in fights that require raw power.
Lots more can be done by the Sharingan.
Then again they say the Sharingan is an evolution of the Bayakugan
Perhaps the Hyuugas have a few more tricks up their sleeves that we aint seen yet.