Sometimes PayPal can turn off potential buyers… If you are going wholesale (versus retail) I would force your decision and push you into a Merchant Account (w/ Authorize.net or LinkPoint) as a solution.
PayPal and Google Checkout are decent, but as noted above they can be painful when dealing w/ Customer Service. And chargebacks - forget about it with PayPal/Google Checkout. You’re much more likely to lose when either of those services are employed. We’ve had great chargeback response on our referred merchant accounts.
Also, lose AmEx. They charge exorbitant rates (fees) to accept the card, and 99% of the time will side with cardholder in any dispute. Stick w/ Visa/MasterCard and add the Verified by Visa and MasterCard Secure Code programs - makes an unbelievable merchant friendly setup (and lowers your rates too!)