First of all, The T2i and the G1 are very capable but are in fact very different cameras. On one hand, the T2i has a traditional SLR design: optical viewfinder with interchangeable lenses; the G1 is an Electronic Viewfinder Interchangeable Lens (EVIL) camera. There are advantages and disadvantages to both designs: Optical viewfinder offers real time viewing without delays, but the pentaprism/mirror assembly makes the camera larger. EVIL cameras uses an mini LCD screen inside the camera in place of the optical viewfinder. The benefits are two fold: cheaper to make, and smaller/lighter camera.
Which one is better? As with most things in life, everything has its good and quirks.
Advantage for the T2i over the G1 include:
- 1080p movie mode -- this is the primary reason I bought the T2i
- Beautiful 3" 1 million pixel LCD
- Slightly better image quality, especially in high ISO
- Focuses faster, especially on tracking focusing
- Faster frame rate
- Selection of lenses
- Swivel LCD screen
- Electronic Viewfinder (only an advantage if you use manual focus lenses a lot)
- Smaller and lighter with kit lens
- Very short lens to sensor register. This means it can take all kinds of manual focus lenses though adapters (an advantage only if you are a fan of manual focus lenses)
- Less expensive with kit lens.
Please keep in mind that these are my opinions. What features you are looking for is probably different than mine.
Side by side from top. The Canon is chunkier. Notice the pentaprism housing. This is what makes the Canon larger.
Side by side -- the Canon is taller but not by much.