I used to think paintball was cool. Then I discovered airsoft. Then I bought a gas-blowback Beretta M9. It kicks ass. So I literally just bought a Marui M-4 and $500 worth of milspec gear.
Yes, you can argue that paintball and airsoft are both just as 'good' or fun, but I think there are some important advantages to airsoft.
1 - Price. Everything is CONSIDERABLY cheaper. 2000 rounds for less than $20. A full-auto M-4 costs less than $300.
2 - Accuracy. Airsoft guns are very accurate for smoothbore guns. You won't need as much ammo. The best shoot an 82mm group at 20 meters. Built-in hop-up kits function like the Flatline barrels for paintball.
3 - Bulk. No hoppers, tanks, full-face masks, or big-ass ammo tubes.
4 - Realism. If you are into that sort of thing, there's obviously only one way to go.
I can only think of one advantage for paintball. The ability to mark someone out.
As long as you don't play with sore losers or BULLSH!TTERS then paintball has no advantages in my eyes.