I've heard good things about stripe. Hopefully they don't freeze accounts after a sudden influx of cash like paypal do causing issues like this.
In the recent .net article 'Burned by Paypal' about this they mentioned that paypal were declining card payments by buyers who were not paypal account holders without letting them know why exactly, making it look like there was a problem with their cards. The error message was 'The credit card you entered cannot be used for this payment', which results in lost sales if the site owner isn't able to follow up with the customer.
I used Paypal for years. Recenlty, got a real merchant account and never look back.
Lower fees and now I have full control of who/when/how over my payment. It's frustrating when Paypal put a hold on my payment and reject my clients for no reason.
Stripe can store credit card details for your customers with no additional charge or expiring tokens. This makes recurring payments even easier than they are with PayPal.
The visitor doesn't need an account with anyone, they just enter their credit card details.
You aren't using PayPal, so there is no risk of them freezing your funds.
Having signed up with Stripe and with PayPal for my business, I can say that Stripe was much easier and faster.
Stripe is a much simpler service. This is obvious in their control panel where you can easily see the information you need, relevant logs, etc. PayPal has many more screens, hidden sections, and details that you cannot see.
Stripe pricing is the same as PayPal's most expensive tier. Past discussions with Stripe have indicated that lower tiers may come in the future, but for now, what you see is what you get when it comes to pricing. (*Note: PayPal does charge an extra fee to store client CC details and do recurring payments, but I suspect this only matters for new or tiny business concerned with a $30 charge.)
Stripe is only available in a few countries. Last I checked it was the US and Canada, but they are working to add more.
PayPal does seem to have more robust fraud filtering. Stripe has sent me an email regarding suspicious activity from a customer in the past, but they don't seem to have anything like PayPal where you can automatically have some payments rejected.
Bottom line: Stripe would make a great addition to XenForo and shouldn't be too complicated to add. I suspect it is even possible with a plugin.
Another - and perhaps the strongest argument in favor of Stripe (of anything other than PayPal) - is the sheer number of users who believe that a PayPal account is required to submit a payment via the service.
I can't tell you how many times I have been asked how someone can sign up to my site's Premium service without a PayPal account. No telling how many more simply give up altogether after being intimidated by PayPal's payment form.
I'll admit that it has been about a year since I made extensive use of PayPal... all I remember is that I was paying $30 per month and that any card token stored longer than a year expired without any warning which caused a lot of issues. I also just spent a while on their site and couldn't figure out if this was the case or not... In fact comparing their Payments Standard/Advanced/Pro options didn't even show many obvious differences between the plans.
It's good to hear PayPal has improved... and a few days ago I was reading that they are planning to "update" their account freeze policies, but more options are never bad. If/when I purchase XenForo, I may put a plugin together to enable Stripe payments.