Which to use first?
 

Should I put on some Rotosounds or Lo Riders? ^_^

Rotos baby. Accept no substitute.

Rotosounds.

I've never used either... you should try both.

For comparing strings I like to string up B, A and G with one type and E and D with the other type so I can really hear the differences.

Rotosounds. The first roundwound on the market, and 50 years later, still the best.

I don't know what the main differences are, but If I were trying those brands, I'd try Hi Beams or Fat Beams, personally. I know that Rotos are my tone, and I love them, but I'm just so damn curious about DR. Everyone loves them, and a friend with them gets a really nice fat tone.

that's just me, though.