What year? They are VERY VERY solid boats. The pre-2003 boats ride like a tank. In 2003, Sonic started the vacuum bagging 'Infusion' process, and a few boats had a few issues, but nothing that cracked them in half. You won't be the fastest boat out there with like power, as compared to a 35 Fountain ()/32 Sunsation, etc., as all Sonics have deep, straight, solid V-hulls (no steps ever). However, you will find a 31SS to be a GREAT boat, with a big cabin, wave crushing-comfortable, runs great with twin BBC power, and is not so heavy to be a Bravo eater. You will find a lot with 496 Mags/HOs, 502 Mags, 500EFIs, and a few with 525EFIs. The 31 is the most popular boat sold by Sonic. Now that the company has changed owners with management that wants to build boats, Sonic will be coming back stronger (and with new updates) in the next couple years.
If you are in the market for this boat however, you ought to take a look at the 32 Active Thunder. They are slightly larger (Sonic 31SS counts the swim platform/32AT is 32'-ish to the transom), and definately faster (if you are in a step-bottom AT) with like power. The new 33 Active Thunder should be in the water by the 2006 Miami Boat Show timeframe as well.