I use a Focusrite Scarlett 8i8, but also have the Scarlett Solo.

Both are very good in my opinion.

If you are just looking at recording your guitar into a DAW (I do that as well, and record each of my practice sessons) You may want to look at other options.

I use the Line-6 Spider V MKII 240 2x12 amp and it has a USB audio interface built in (I assime the smaller model may have this as well) So i plug in my guitar to the amp, plug the amp into USB on my PC, and then selece the MKII as an input on an armed recording track in my DAW. It records it perfectly, but I can also still hear it from the amp as I play.

If your amp only has a line-out, then yea, you woud need a Audio Interface to acomplish the same thing.