you can tell if it's a regional by the flight number, typically a regional airline flies for a major under a 4 digit flt. number, usually something like 3xxx, 4xxx, 5xxx,
and the aircraft is also an indicator if it is a regional carrier or not. the bigger aircraft that fly in and out of BUF are b737s, a319,320,321, b757, dc9, b717 etc... those are the aircraft flown by the majors.
if you aren't sure and are a nervous person, just book a flight on southwest and call it a day. they do not have any regional feeder network and only fly b737s
the biggest problem with regionals is the whole airline heirarchy scheme. the regional pilots are getting paid sh1t for wages (many make around 30k annual) and are always on the road and work crazy hours. they are more or less putting in their dues to accumulate pilot in command hours of turbine aircraft to work up to the majors. Many regional pilots are very good pilots, but they are in a difficult situation, not making much pay, not as knowledgeable and experienced etc...