What class are you going to shoot in?
Tac Irons/ Tac Optics:
Most common shotgun you see in 3 gun is Benelli M2 because they are tanks. @ $1,000
Remington Versa Max is what Daniel Horner #1 uses. I really like this gun with the gas system design but it isn't as proven as the M2. @ $1,000
The Jerry Miculek 930 SPX is a great value but it isn't ready out of the box. You still need to get a filled lifter and it helps to have it drilled out and polished so you dont cut your hand up. You will need to do these things with most any gun out of the box. @ $600
Open:
Siaga (they are famous for not working)
MKA 1919 Pretty new to the game but Firebird precision is making some awesome ones for under $2,500 finished.
Any of the guns above with x-rail system.
I spent a day shooting a 930 SPX JM and didn't have a single problem but the more expensive M2 might be the best bet. Try to get a used one for cheaper its better then buying a shotgun then regretting it.