I'm an on-and-off user of around a dozen aggregators, which should make me a fan of separate context menu items, but it doesn't. Right-click-subscribe should be an extra-quick, simple, direct way to subscribe, and choosing which menu item is the one you currently want isn't that. Also, having built .reg files to remove right-click BlogThis items for Blogger (which never bothered to provide them), I know a bit about how the standard instructions for removing a context menu item ("first, backup your registry, because editing it can turn your computer to slag; next, run regedit, and be incredibly careful, because a mistake can turn your computer to slag; ...") strike most people. With a single standard "subscribe in default aggregator" item, if something goes horribly wrong with Feed Bandit, they can just switch to a new aggregator and keep using the same right-click, plus when they hand off their work computer after going through six different aggregators, they'll only have to remove one item to hide how much blog reading they've been doing at work.

I agree that the menu item shouldn't be tied specifically to RSS Bandit. But, a simpler text label would be "Subscribe to this feed". You don't need to mention that it will subscribe in their default aggregator. Does the menu say "View Source in default source viewer"? No. There is an implicit contract that the user's choice of external tool will be used.

I'd vote for "Subscribe".

I'd prefer 'Subscribe in aggregator' with the feed opened by whater is handling the URI scheme.

"Subscribe to this feed" + 1

I think that from an end user's perspective, it's better to say "Subscribe in RSS Bandit". Applications should remove things like IE context menus when they uninstall, if they don't, they have a bug and should be publicly pilloried for it (Installation rule #1, provide an uninstall. Rule #2, if your uninstall leaves links to your executable after it's been uninstalled, you look incompetent, with good reason). I suppose "Subscribe to this site" would work, but then if there's a "standard" wording to the menuitem, you have apps competing for the same menu item, the way every image editor competes to be the default .jpg handler, or you'll have duplicates - I'm not sure whether you can create context menu items with the same text. If you've got duplicates, then the end user will never figure out what the correct link is when multiple aggregators are installed, while if aggregator X gets uninstalled but leaves a dead menuitem, the user has a chance of figuring out the right thing to do. If you go by menuitem wording to figure out what item to link to, you've got an i18n issue, how many ways are there to translate "Subscribe to this site"?

I think it should be "Subscribe to RSS Bandit" (if RSS Bandit remains as name!)... An end user should be able to remove from the context menu... RSS Bandit should prompt if it should install a link to the context menu at install though... this way it is not intrusive... intruding is bad software... and RSS Bandit is good stuff...

Personally I'd prefer the "Default Aggregator" aproach, since the feed URI scheme itself will be using the default aggregator. I'm happy to see you're doing it for firefox too!