Reviews seem polarized on the Subaru CVT. TTAC and some others hate it, and some love it. I hated it. I just didn't feel the "rev high and set off" suits the torquey boxer engine, and (now, I've only driven one) the NVH made the chain system more than obvious.
For the OP, the 2010 Legacy is all new. Subaru rarely changes engines, just updates them, which is actually nice as you know that they eventually get sorted out. The 2.5L four and 3.6L six have been around in their current form (few changes) since 2005 and have a terrific track record.
Subaru had some 6-cylinder issues a long time ago, but in about 2001, they came back with a 3.0L six, and then the 3.6L six, and both have proven among their best engines, period. Given how a boxer mounts in the car, length is a concern, so they shortened the engine by using timing chains instead of belts, and solved a source of aggravation for previous Scoob owners. However, the current 2.5L (and all from 01) have 168K belt intervals, so it's not the big deal it once was. (Subaru timing belts are among the most expensive to change)