I like the MSR ultralite towels because they are the lightest. I use the L and XL size, however have the M size for travel when I don't need to wrap myself in the towel.
I don't like the felt towels because they need to be stored in ziplocks or else they dry into cardboard.
I also find that really thin cheap cotton towels (i.e. the disposable variety from Japanese spas) or the woven Turkish hammam towels also work well.