A friend of mine wants to know if he should get this or this guitar. sorry to bother you all with a question that must come up daily on here but I don't have a clue.
both very tonally different guitars... the strat will give a brighter, more delicate sound, and the SG would probably give a fatter, rounder tone.

depends on what he plays, but I personally would go with the strat.
What kind of music does he play?

They do both sound very different. He should really try out a few Strats and SGs in a shop and decide by that.
Well they're two completely different guitars. If he's gonna be doing alot of heavy distortion and all he oughtta go with the SG. If he's gonna be doing alot of bluesy stuff or music that requires more clean tone he needs to go with the strat. Also, the SG is made in the US, where as that model strat is made in mexico, however ive played the DP strats and their pretty sweet!
I would say if hes playing blues/rock/funk (RHCP, Pearl Jam, SRV, John Mayer, Standard blues, Jazz) Id go with the strat. If youre doing anything involving lots of gain/modulation and/or effects, the SG is the way to go. Id go as far to say that they are equivalent as far as playability, its just a difference in sound.

American Strat
Epiphone Valve JR head - Volume Mod'ed
Custom 1x12 with Private Jack speaker
Boss BF-3 Flanger
Boss DS-2 Distortion
Boss MT-2 MetalZone

Gretsch Acoustic
TS, if you decide to go the strat route, can I suggest a Classic Players 50s instead of the deluxe, you can knock the price down off of them to around £420ish, and its a FAB guitar, with an awesome neck.