http://blog.unibulmerchantservices.c...ment-services/
You are asking the difference between having a middle man process your payments (3rd party processor) vs having your own direct merchant account.
Having your own merch. acct is going to be cheaper to process payments, but you will have to deal with customer service.
If you aren't pushing much volume and/or don't know what the fuck are you are doing in the business world, just pay a 3rd PP.