me personally,
i loved doubled guitar parts,
panned hard left and right,
and actually played.
unless it's super tight metal,
i prefer the rhythms to be a bit looser, not super tight,
each with their own tone and personality.
i will typically change guitars, pedals, amps, speakers, mics, anything and everything to give the individual track what it needs to stand on it's own sonic merit.
i am a firm believer in real amps, real effects (that are guitar specific, such as distortion, vibe, wah, etc)....
prefer micing cabinets and getting room effect into the track,
but do use direct capture devices quite a lot, for blending with miced tracks and for increased clarity.
rehearse the parts until you can play them without thinking about it...
so when the red button gets pushed, all you are doing is channeling vibe.
do experiment with mic positions A LOT,
and when double tracking, by all means, play in tune.