I have data on WIND, Mobi and Bell (and used to have Fido, basically Rogers). I can say that Mobi has consistenly the slowest speedtest results in Greater Vancouver. But I mostly use a Blackberry now or dumb phone on Mobi so it is not a big deal (but still during app updates etc it is slow). I'd never rely on Mobi's data if I have a choice. And also this is one of the reasons most of my friends won't want to sign up w/ Mobi if they need data. WIND is much faster (although not fastest) at least here.
No longer on a leash by Fido