Shall I arrive along pre-paid tour or would it be easier&cheaper to get to Guilin by myself?

In my opinion, travel on your own is much cheaper than join a tour. But if you join a tour, they will arrange all the details for you and you do not worry about it.
If you want to join a tour, I think TraveChinaGuide is a good company and they can arrange your trip based on your requirement. I like the company very much, since I join their tour on the Li cruise.