I won't generalize so I'll give my opinion with a little background for each side.
Pros:
I love my Country Fido (with free Rogers roaming). To me it's better than sliced bread and I'm very happy to have it. I wish that everyone who wanted the Unlimited Canada could have one. My plan aside, the unlimited incoming plans are great too. Fido beats the competition hands down on plans and rates. I hope they don't change too much. Rogers knows that people who leave Fido are likely destined for Bell and Telus so I think they keep a good balance to keep the customer away from CDMA.
Cons:
It's funny how we always hate a company when our service or bill is screwed up but we love them when things go smoothly. I had some major problems with billing and technical in the first 7 months of being a customer (to the point where I could have ripped my hair out and cry lol). Now, so long as I don't call them and they don't call me we have a middle ground where they provide the great service plan and an error free bill and I provide payment in a more than timley fashion.
All in all, I think that if you're lucky enough to not have tech/bill problems then Fido is Canada's best choice. If you are not so lucky, then you're in for a rollercoaster ride until the problems are ironed out.
All in all, Fido may be a little bumpy but their still well worth the ride.