If you're into:
Gaming performance -> G53Sx
Better speakers, better and higher resolution screen (and also warranty coverage if available) -> XPS 15

The Asus N55sf (i7) is not really worth it for the price paid... perhaps you can consider HP Dv6 instead, which is also a good choice 

since you don't tell your budget,
get the xps 15 with fullhd upgrade, good speaker + good screen + backlit, if you need more performance, maybe can upgrade to i7-2630qm, cos im not quite sure how intensive your designing and video editing will be.
since you are not hardcore gamer, gt540m should be suffice to handle all the latest game at medium, high setting.
my 2cents 

like what sifu said, can also look into hp dv6, stronger gpu for gaming. not sure about the pricing, but this should be the retail price

G53Sx-SZ039v, i7-2630QM + Nvidia GTX560M (2GB)@RM3999, backlit keyboard, gaming backpack & mouse
Dv6-6001TX, i7-2630QM + AMD HD6770@RM3499 [2.63kg]; Beats headphonesN55Sf-SX047v, i7-2630QM + Nvidia GT555m (2GB) + Bluray@RM3699[Bang & Olufsen]; USB3.0, Sonic Master subwoofer
N55Sf-S2043v [black], i5-2410M + Nvidia GT555m (2GB) + 1600x900@RM2799[Bang & Olufsen]; USB3.0, Sonic Master subwoofer

G53sx should satisfy ur needs except the sound.... maybe u can consider getting a good external 2.0 speakers.. then G53sx will be ur best choice.. i too may get a new lappy and at 1st my requirments were what u hav written above... in the end, i've decided to go for G53sx... (may only purchase it in dec though.. but will be reading reviews 1st...) for the sound, i probably will pair it with a good 2.0 speakers as 2.1 speakers is kinda bulky.. take note, the GPU in g53sx sz is 128bit and not 192bit.. some suggest that it has the same performance as the current G53sw (460m 192 bit)
xps15 does  not provide numeric keypad.. only alphanumeric... g53sx and n55 has the numeric.. well, dell lappy lately seems to hav quite a few issues... <- correct me if i am wrong.. i hav no intention to hurt any dell's fan ...
these r all mere personal opinion..
well the best way to see which of the lappy that u life most for feeling of the lappy, the build quality, it is best that u try them out in a comp shop... cheers..