The towel grip has a better absorption of sweat. Compared to synthetic grips you may have a slightly damped feel. Also you have to change the towel more often then a synth-one! At my actual terms (in direction colder) i prefere the synthetic grip!
For the towel grip, I find it too slippery unless you have sweaty hands. My hand doesn't sweat all that much so :\ doesn't work for me. So in my personal preference, I like synthetic grip better.
The advantages from using either towel or synthetic grip correspond closely with the player's own preferences in regards to the aspect of how comfortable does the player feels using it and influences the performance of the player's gameplay. If you feel that using a towel makes your grip on the racket more comfortable and facilitate a more solid and confident feeling of racket swings action then, that grip will yield more advantages to you regardless what people commented about its disadvantages.
It's all about personal preference... For me, I prefer towel grip, but I always need a few sessions, before I deem it to be in prime condition for use in tournaments, so will change it the session before hand...
again, its a matter of preferrence. however, it does chafe my skin more when I use a towel grip. plus i hate it when it hardens after the salt from your sweat builds up on the towel grip :S
i personally choose a towel grip as it has a better grip even there is no sweaty hand, i couldn't understand why some people say that towel grip for less sweating person are slippery.
It is actually the players who have a softer/lighter grip (with more emphasis on finger tip power) of the handle that prefer the towel grip as it does not have tackiness at all unlike all of the synthetic grips. Synthetic grips are for players who grip the handle slightly tighter (with more emphasis on middle finger contact), where tackiness is more important.