Grand Central Station of Aegean. Most boats stop here and you can make connections to the Dodecanese and even Samos. Town is full of foreigners and bars and also internet cafes. Head for the smaller villages or Antiparos if it is quiet you seek. If you like to party then Parakia and Naoussa will suit you just fine. The tiny idealic fishing village of Naousa is so crowded in the summer that you have to stand in line to walk past the cafes that surround the port but it's a great scene and worth going for Mykonos-like action without Mykonos prices. The beaches of Paros though popular are also quite nice and Paros is known as the wind-surfing capital of Greece. Plenty of camping too. 

The ferry trip is about 6 hours from Athens and stops Syros sometimes. There are daily connections to Mykonos, Ios and Santorini and Sifnos in the summer. There are also less frequent connections to Crete, the Dodekanese, Ikaria, Samos, Amorgos, the small Cyclades islands, Skiathos, Crete and Thessaloniki. There are also Hydrofoils, Catamans, sea-jets and other strange and speedy craft that stop at  just about every island around. The travel agencies in the port list the daily boats and this is about the only accurate way to keep track of them all. 
 
Antiparos has nice beaches and cafes and is more relaxed then Paros. There is also the gigantic Cave of Antiparos which is the most popular site on the island. There are ferries connecting the two islands leaving every half hour or so from the town of Pounta, plus excursion boats that leave every morning from Parikia