Wow, dangerous question. (Everyone has their favorite and will defend it like a mother bear protecting her cubs) I can predict the future and your about to hear lots of Aldora, Blue XTSea, Dive with Martin, Tres Pelicanos, Blue Angel, and my personal favorite, Blue Magic. Not sure where Villa Grace is or if they have their own pier, but if they are south of town, most shops will pick you up at a hotel pier if the hotel will allow it. Some charge a fee.
Cabs are cheap in Coz, so you may need to take a cab to the shop for departure or to Caletta Marina far south of town where most operators that don't have their own pier leave from.
Email your choices of dive shops and see if they can accommodate your request. The main differences will be tanks with the standard being aluminum 80's with an up charge for al100's. Aldora does steel 120's I believe. Most will utilize 6 pack boats with less than 8 divers, beware of the cattle boats. The other difference will be where they do a surface interval, boat, beach, or club.
If if you are bringing your own equipment, ask for "valet" service for your equipment so the operator will store, rinse, and haul your gear during your stay. Some charge, some don't.
You can't swing a dead cat in Coz and not hit a dive operator and except for the cattle boats, you almost never hear a bad report. Some of the ops that are run by the cruiselines have had some bad reports.
Christi (Blue XTSea) and Dave (Aldora) are frequent contributors to this board and run excellent operations. They can give you almost immediate, firsthand, and up to date knowledge on Coz so they deserve a chance for your business. All of the operators will accommodate reasonable requests that I have found.
good luck and safe travels, please post a trip report on your return. Eat the scallops at Guidos and drink lots of Bohemi Obscura for me!! I'm landlocked for a couple of months.
Jay