I use Questrade, and Mat uses RBC Direct Investing.
I really like Questrade, robust trading platform and commissions start at $4.95. Their IQ Edge desktop platform is going to trump pretty much anything you see from the major banks. So if you are truly looking for a "trading" platform, they'll likely be it.
I used to have an Interactive Brokers account, but this was quite some time ago so I'm not sure how they've progressed over the years, but I know they are for sure the cheapest level of commissions. They are a true penny a share commission platform, whereas Questrade advertises penny a share, but it's $4.95 minimum. So if you trade 600 shares, you'll be charged $6 for example.
Overall, I've been a client of Questrade for over a decade. I really don't think you can go wrong. And, if you're adamant on sticking with a big bank, which a lot are, RBC Direct Investing from what I've heard is the best major bank platform.
Keep in mind, we do have an affiliate code over on the blog for Questrade. If you use the code stocktrades50 it will get you $50 in free commissions as long as you make 10 trades in your first month I believe. Full disclosure, you get $50, we get $70 from Questrade.