R300's front and back will give you a more consistent soundfield, and would definitely be the better choice if you use a Pioneer receiver as they have a single crossover point for all speakers that set to small.
If you go with the R500's for the front, I would house the R600c centre if you can as it's cabinet volume is closer to that of the R500's, and you'll gain from it's extra capabilities (at all volumes). You could use the R100's as rears for these, but you'll need to be using a receiver with multiple crossover points so you can choose one independently for the rears, centre, and fronts. I would usually recommend a single crossover point anyway as this means that all speakers (regardless of their size and capabilities) wil be reproducing tha same frequency range, giving a more consistent soundfield. Using R500 for the fronts will be of benefit if you are also using the system to listen to music.
Which receiver are you using or going to use?
Different. You'd need to hear for yourself to see what you prefer.