Is it better to join a wine tour or explore the wineries on our own?

We will be in Mendoza for three days and would love to know what the best restaurants are and which wineries you recommend. I love sweet wine - think Moscato, sweet Riesling, port, are there any wineries where I will be able to find something comparable in addition to great reds and whites?

Any information would help! 

Mendoza (Argentina)   Argentina