I did some comps about a year ago, looking at setup fees, processing charges, %'s etc.
Paypal charged more per transaction, but without one time setup fees, and monthly service fees. If you were doing a lot of monthly volume (dollars and transactions) the other services were cheaper than Paypal.
Since you are just getting started, will you be doing thousands of transactions each month? (I'll guess no

) Paypal is hard to beat in the lower volume sales. (as of last year... I haven't needed to re-run the numbers)
Build a spread sheet and look at how much it costs to do 100 sales per month, 500, 1000 (you decide where you want to go) and put all the costs together and divide them back out to see the real cost per transaction.
It makes a difference if you are doing 100 transactions at $20 verses 2 transactions at $1000 each.