That Riccar canister is quite nice, though without a power nozzle, it won't be adequate for carpets.
The Kirby Heritage II is *very* nice, and it should also be able to take the new Kirby Generation HEPA bags. Those filter better and provide better airflow than the older paper ones. For carpet cleaning the Kirby and Royal will both perform exceedingly well (few vacuums of any age can beat them), but you're right, the Kirby attachment system is cumbersome, and the Royal one is, if anything, worse.
If you're looking to buy new and keep it inexpensive, my top choices would be either the Riccar Radiance or Simplicity Symmetry for an upright, with models available for about $250, or else, for a canister, the Panasonic MC-CG902. For an upright without any attachments, Sanitaire is outstanding - but more so than Kirby or Royal, they do carpets and large rugs only.
If the budget is higher, there are even better options available: the tandem-air uprights from Riccar/Simplicity, Sebo's Felix and Automatic X series, Miele's S5 canisters, Riccar/Simplicity canisters (best out there, I think), Sebo's D- and K-series canisters and several others.
If you're not averse to eBay, you might also look for a used TriStar CXL or DXL.
