With all taxes being equal and market returns being equal, RRSPs and TFSAs should end up at the same value at the end (to clarify, the same value when withdrawn).
The problem with the TFSA is that it's too new and growing at $5500/year (as of this year), which doesn't take long to use and max out.
The common answer for when to invest in your RRSPs is when you move up to the higher tax brackets. Obviously any tax bracket higher than what you expect to be at when you retire will work, but at the end of the day it's for you to figure out.
There's another argument, that isn't mentioned much, but has been talked at the Canadian Bogleheads forum. I can never find the thread, but the discussion is an argument to invest in an RRSP at a lower tax bracket, to help keep your income in a low tax bracket where you'll receive more government subsidies, like GST/HST refunds, child credits, etc. I honestly don't know the argued government benefits off the top of my head as I live in Alberta and just a childless guy. Ontario on the other hand, with more tax brackets and more complicated tax system, with credits, subsidies, health fees, etc can have a lot of hidden benefits.
Food for thought.