AT&T
You have to get the X10a (I believe this is the rogers version). This X10a will have the 850/1900 3G band. Your plan will be more for the same amount of minutes + unlimited texting ($20), and the Dataplan ($25) but you get roll-over minutes. Advantages of AT&T - some coverage is better (outside of major cities)
T-Mobile
X10i is the phone (uses 1700/2100 band) . I can vouch for this, since its what I use. The 3G is fast (streaming music or youtube). You'll have to get the Android plan (same as a MyTouch). You'll loose 3G if you are in certain areas that aren't close to a major city and in certain deadzones.
If cost is a factor:
AT&T = 900 minutes + talk & Text & Datapro (2gig) = $105 month
T-mobile = 1000 minutes+ Talk & Text + Android = $70 month