Airsoft vs Paintball

Despite the title, this isn't a real "versus" type of post. This is more of a comparative summary. Granted, I've not gone out paintballing, but I've been around enough to get a rough idea...enough to point out the key differences.

First off, you have two totally different types of equipment. Paintball markers generally look like sci-fi ray guns. They have a CO2 cannister, and a hopper unit for the paintballs. Paintballs themselves are generally .68" in diameter, though the sizes vary. They're filled with paint, and explode on impact.

Airsoft guns, on the other hand, look like real guns (granted, some are clear plastic...some just look like plastic, but some are full metal). They are all powered by some sort of spring mechanism pushing air to propel the BB, but they can be straight spring powered, CO2 powered, green gas (propane) powered, or battery powered. The BBs are solid plastic 6mm balls, with the most common weight being .20gm (though, I play with .23 and know people who use .43 in spring snipers). Generally, the more FPS (feet per second) your gun fires, the more weight you want to keep them from going completely out of control.

Paintball is pretty easy to tell when you're out: you have paint on you! Sure, there are "wipers" who will wipe that shit off and cheat...but there's also refs on the field!
Airsoft is a game of honor: you call yourself out when you get hit. Sure, you can be a "rhinohide" and not call yourself out, but guess what happens when you're not calling yourself out? You keep getting lit up. Getting hit a few times by a .20gm plastic ball flying at 375 FPS sucks. Considering that some of the airsoft guns are firing 20-30 RPS (rounds per second), a quick 2 second pull on the trigger can send quite a volley downrange. Don't think "Oh, I'll get hit once and call hit and that's that!" Plan on "I'll get hit by a volley and yell out hit hit hit while raising my red rag and hope that they stop after a few seconds."

Does paintball hurt? No idea. Never been hit by one. I've heard of players freezing their paintballs to make them hurt...but, I've never been hit by one.
Does airsoft hurt? Well, sure. It can be a bee sting. It can also hit the tip of your nose or finger and you'll be swearing a blue storm. I've had friends get teeth shot out. I've seen them (firsthand) embedded in people. I've (personally) broken skin, both by getting shot and by shooting others. It depends on where you get shot, how far away, and what protective clothing you have. Once, as the "on-field medic" I cleaned and dressed about 20 hits clustered in an area that looked like a swarm of hornets went to town on the guy. I've also had hits that I actually stopped and said "Uhhh, did I just get hit?" as I was raising my red rag to call myself out.
When in doubt, call yourself out.

Safety gear is the same for both: full seal eye protection, gloves, face protection (to reduce chances of teeth getting shot out).