Reasons to buy the Nikon D5100 
- Low noise at high ISO 1 183 ISO
- Great color depth 23,5 bits
- Great image quality 80.0
- Wide dynamic range 13,6 EV
- Longer battery life 660 shots
Reasons to buy the Canon EOS 600D 
- High resolution screen 1,040k dots
- Built-in focus motor Autofocuses with more lenses
- High true resolution 17.9 MP
- Shutter lag @ 283 ms
- Longer battery life @ 440 shots
(Walaupun saya Mr. Canon user...tetapi dari segi 'technical wise' di atas terutama pabila merakam Astrophotography nampaknya Mr. Nikon D5100 ada kelebihan sedikit. (Maaf..just my point of view, correct me if i'm wrong) 