I've heard a lot of horror stories about Paypal, although I haven't experienced them myself. However, I think it would be beneficial to get recommendations for payment processors. Any ideas?
Im not sure what you are charging for or what your business is, but beware that Braintree routinely turns down businesses that their underwriter considers 'risky'. MANY Web2.0 businesses fall into this category. Social networking, some SaaS, online dating, etc.
You may have to shop around to find a payment solution that fits your business. Just a heads up.
Firstly what is your product or service? It probably makes a difference who you would choose. For example, if you have subscription payments then Google Checkout isn't in your space (yet). PayPal is an obvious one and I think you can hear "horror stories" about most of them in my opinion - how would your customers perceive you offering payment in PayPal. In theory it could be a negative. Where are you located? Are you wanting to offer in Dollars, Euro, Yen? Give us some more info on what your service/product is and we can help you some more.
I coincidentally met one of the principles of Dharma Merchant Services when I was considering which way to go. She was incredibly upfront and didn't push her service ('look at other options and let me know if we can help').
I try to make decisions relatively quickly when the consequences are mild for a sub-optimal solution so that attitude sold me.
The only thing going for Authorize.net is that it is supported everywhere in every language and every framework. And, of course, they aren't actually a merchant services provider. They are just a gateway service. You need both to accept credit card payments (if I could find a company that did both really well, I'd switch to them).
Authorize.net is a bit pricey and a bit difficult to use. But, it is the gateway service that we currently use...and when I switched to another shopping cart, we didn't have to change gateway providers or write new processing code. Which was nice.
When we write our own shopping cart (which seems impossible to avoid, because everything we've tried is such a poor fit for the way we sell our software), it won't tie into Authorize.net. It'll use PayPal, Google Checkout, and some other payment gateway (whichever one works with the cheapest merchant services provider, while still offering recurring payment support, probably).
Also, I'm surprised that ProTX ( http://www.protx.com/ ) hasn't been mentioned on this forum. Anyhow, whatever you pick, it'll probably be cheaper and more responsive than WorldPay.
They offer everything the big dogs do, but their staff is incredibly helpful and attentive. We use them on FamSpam and GitHub.
I wouldn't find the merchant with the lowest rates, find the one you like the most. As your business grows, you can always renegotiate your rates.