Bookshelf vs floorstander. In the lower price ranges bookshelf plus sub will be much better than floorstander alone.
Receiver vs amp....hmmm you still need a pre-amp with an amp or are you speaking of integrated amps? Be specific. Tbere's a lot of stuff out there. An avr (audio visual receiver) is a pre-amp/tuner/video processor/amp package. An amp is just that, an amplifier, still needs a pre-amp and sources. An integrated amp is a pre-amp with amp, but no other sources built in, just the facility of switching your sources.
Personally many avrs will work quite well for you and offer a great bang for the buck. Most people buy avrs so that's where the economy of scale lies, you get more features in a better $ package than separate units can offer...generally.