So, if you currently offer multiple feed formats, may I suggest that you stop doing this? Just pick a format - any format. If RSS does what you need, stick with it and dump your Atom feed. If you need the extra features that the Atom format offers, dump your RSS feed. Either way you'll be fine, and your readers will be happier.
And if you're just starting out, pick one format and forget about the other one. It doesn't matter to your readers which one you choose, so there's no need to agonize over the decision (and you can always switch to the other format later on).