Reasons for Nikon D5100:
-Higher ISO (which I understand helps me capture moving people better)
>> Yes, to a point. You will still need 'good' light to get good pictures. If only high iso was needed, everyone will be using green colored night vision cameras

Most cameras released from 2010 onwards have very good high iso performance.
The D5100 does use a nice high iso performing sensor though, which imo is better than one for the 600D. However, it has very little significance at normal viewing sizes (eg. your monitor or 50" TV).
-Less noise on high ISO (according to snapsort)
>> One advice, Snapsort is a lousy site. Its no more than a brochure compilation. No sample shots, do real user review.
You already know od DPR, try Imaging Resource as well.
http://www.imaging-resource.com/IMCOMP/COMPS01.HTM
-More dynamic range (which means colours are nicer yes?)
>> No really. It just means that more exposure levels (ie. brightness levels) is captured with a single frame.
-Faster FPS
>> Most DSLRs as of 2010 will have enough.
Reasons for Canon 600D
-Images are softer and thus nicer for people shots
>> Not really. Need to use better lenses for the 18mp sensor. Not apparent at normal viewing sizes anyway.
-In-built AF motor (hence cost savings on lenses in the long-run?)
>> It does not have a built in motor. Motor is on the lens for all Canon lenses. Its Nikon that has some lenses with motor and others w/o. The D5100 btw, does not have a on camera motor, so you need lenses with a motor (designated as AF-S).
-More user friendly for newbies to learn and start out with
>> Really depends on user getting used to each brands system and preference.
To me Pentax has a very good UI and photographer oriented interface (superimposed histogram; WB and pict style preview and saving; single button reset to default; AF calibration; etc)
So depends on user.
-According to friends, based on experience it performs better in low light even though specs seem to favour the Nikon. ("Higher ISO does not necessarily means the pictures come out nicer")
>> As mentioned above. No that relevant for normal viewing sizes and 'good' lighting still needed for good photos.
Didn't really consider the other brands since almost everyone uses Nikon and Canon so I'd be able to get better help and I'll be able to borrow lenses and stuff?
.
To me, borrowing lenses is a not that good a reason. You'd need to be responsible for your friend's expensive lenses and/or they may be apprehensive of lending to you.
Personally, don't think there is any wrong camera between the two.
Do look at other brands as well if you are looking to get a bit more for your money. (eg. Pentax; Sony)
(Eg. On camera shake reduction; smaller cameras; smaller lenses; in-camera focus motor; etc)