I'd say this should be a case of thinking about what's good for your client, rather than what services you don't like. But also, you may need to know more about the client's online donations. Do they get lots of online donations with a mix of big and small options? Do they get little online donations but of larger values? Do they just get a small amount of donations at small amounts? Are they actually processing no online donations but want to improve their transaction rates?
There are a number of services, and you don't need to process things through Simple Commerce. You could start with the easy services like Network for Good, JustGive, Razoo. These are services built for accepting nonprofit donations. You'd just need to create a landing page in ExpressionEngine that takes the user to the selected service.
Amazon Simple Pay Donations and Google Checkout will also process donations.
Simple Commerce only needs to be part of the process, if you are trying to store transactional history with ExpressionEngine. There are other methods for doing that as well, for example if create an email account for transaction confirmation emails. You can set-up EE to bring those emails into EE for creating a log as well.
Generally speaking, if the nonprofit just wants to accept donations online, doesn't a get a lot of donations (historically), and doesn't get frequent large donation amounts (say over $5,000), then going with a donation service like Network for Good, JustGive, Razoo, etc. isn't a bad option. Obviously, you'd want to tell the user about the 3rd-party site, but many donors are familiar with the three listed.
PayPal, Amazon, and Google Checkout work well for mixed transactions. Donations, bracelet sales, etc. The transaction rates for nonprofits (after qualified) are low. PayPal is simple and easy to use, and typically not problematic for thousands and thousands of nonprofits. If the nonprofit occasionally processes very large donations online (single transaction of $5k, $10k or more), then that needs to be consider, but it provides the least friction for the potential donor.
Amazon services is also good, just like PayPal tons of folks on the internet have Amazon accounts, and using their service to process donations can work. I'm not certain if they allow reoccurring donations (you'd need to check). Personally not a fan of Google Checkout/Wallet mix, but it's viable, not as frequently used, so could halt some donations in their track. You're always looking for that mix of viable, low transaction fees, donor doesn't hesitate to use with nonprofits.
Simple Commerce is the easiest option for tracking both the sales and the donations (I believe you can do like Store for donation, set an item for $1, then use the quantity field to set donation amount 50 items = $50 donation). If the nonprofit really wants more payment gateway options, then I'd look at Store by Exp:resso. They'd have to pay for it, but it pays for itself pretty quickly, if they're handling regular transactions or if you design donation pages that increase their transactions.