I'll just post the differences here...
Ok, so lets say his bail is 1,000 dollars.
If you chose to bail him out, you would have to put up the 1,000 dollars to get him out of jail. Bail is basicaly a down payment to the courts saying that you will show up to your court date and not go on the run. It is fully refundable assuming he shows up to all court dates but wouldn't be given back to you until a couple weeks after sentencing and there's a fair amount of paperwork involved in getting it back. However, if he is found guilty on his charges and he has fines as part of his sentence, they might take the bail money and put it toward the fines.
If you choose to bond him out, you contact a bondsman and usually pay 10-20 percent of what the bail amount is, so if his bail was 1,000 bucks. you would pay the bondsman 100-200 bucks and he would pay the bail. Bond money is not refundable. If you bond the guy out, you will have to sign papers to the bondsman saying if your friend goes on the run you'll help track him down. The bondsman will send a bounty hunter after him and all that shit.
If his bail is over 5,000 or 10,000 obviously you have to still pay 10-20 percent of that but you would also have to put up collateral. (I had to give a bondsman my car title)
Thats pretty much it.