Power output is definitely a concern because we don't know what speakers you'll be using. You should figure out what you want from the receiver, or what you need it to be capable of based on your listening preferences, budget, speakers, number of inputs you need, the amount of maintenance you're willing to do, and your level of electronics knowledge. How it looks should be more towards the bottom of the list. How does one measure their pain threshold? What's the db level of an unwanted late night text from your boss?
Baconbadge is spot on with his comment. I have recently fallen hard for vintage tube gear, and acquired integrated amps, receivers, and stand alone amps from the likes of Fisher, Scott, Pilot, and Grundig. They all have very outstanding sound qualities, and all sound reasonably similar, but yet a bit different. I'm sure the 500C is great, I don't own that one yet.

What I will say, is they could all be end game pieces for me. As Baconbadge suggested, figure out what you have to have, and what is a wish list item. I believe the 500C has a headphone out, and 500B does not. 500C and 800C are very close relations, but the 800C adds AM. If you don't need a tuner, there are lots of integrated options that likely equal the sound quality of the 500C, and maybe even best it. Then there's power output. EL84 output tubes make about 13 watts in most of these brands, and they make some sweet sounding watts. 13 watts can be plenty of power in the right sized room with the right speakers. I believe the 500c has 7951 output tubes (a bit less common than EL84, but NOS and new manufactures make them easy to find), making about 30 watts of power typically. 30 watts increases your speaker choices quite a bit. Phono stage performance varies between these models, and my experience here is limited to my Scott 222B which has a very nice phono stage. I have read the Fishers are pretty good too, but I have no experience with them yet. As mentioned above, unless you find a restored unit with credentials (the terms restored, recapped, serviced, and through the shop are used very loose), anything you buy will need to go in for a full service. Receivers cost more to restore due to the added complexity of the tuner rebuild and alignment. So take all this tell me how anyone can declare which unit is the best. The good news is, with some planning and component synergy, we can all experience very hi levels of sound quality for a very fair price. Most of these pieces of gear will stand the test of time, due to the nature of the design. No complex IC chips to burn out only to find out the stock on those parts ran out years ago, and there is no replacements, or elaborate displays that develop issues with no source for parts. You get the idea. Don't worry about best, and aim for what suits you. Pick one, get it serviced and optimize the components around it to suit your taste.
I will make a wildly general statement, and I hope I don't get blasted for it. In my opinion, as the watts go down, the midrange and high frequency sound quality sweetness goes up. Obviously output transformers, power supply, and other design choices play a part in this, but I believe there is a trade off in sweetness as power goes up.
Onebean