The best TFSA rate is currently at State Bank of India offering 3.35% for a 1YR cashable GIC. You can view all the rates at http://www.cannex.com/canada/english and compare which banks/credit unions offer the best rate.
That rate is the non-cashable locked in rate. The cashable rate for the TFSA Power Saving Account is only 3.00%. Their service fees are also very high. You can't just pick the highest one. There are many factors to consider.