^^ The choice of your glass also depends a lot on your budget. I believe the Canon lens is the most expensive of the lot. Photography guru's correct me if I'm wrong, but the Canon lenses do tend to be better than its Sigma/Tamron counterparts as the glass used in Canon tends to be better. I find the reach of the 55-250 pretty accurate and even at full 250 you can take handheld shots without the IS too, its quite subjective to the amount of lighting you have.
Eg: Check this out....
This is taken at 250mm handheld. So even with a 300mm you can go handheld without the need of a tripod, but its highly subjective to lighting.
Hope this helps!
@Anvay: Showing off raynox chacha
Here's my entry for today....
Click for larger version....
EXIF:
Camera: Canon EOS Kiss X2
Exposure: 0.005 sec (1/200)
Aperture: f/8.0
Focal Length: 18 mm
ISO Speed: 200
Exposure Bias: 0 EV
Flash: Off, Did not fire
Taken a few meters above the road for Khardung La pass.