Spot? Partial? Evaluative? Center Weighted? What mode to use?
I shoot mainly full flash in ETTL mode so i am guessing the metering mode won't matter. How ETTL works (from Canon site):
Canon's flagship flash mode, E-TTL stands for "Evaluative Through-The-Lens" flash exposure control. In E-TTL, the meter reads through the lens, but not off the focal plane. Utilizing a preflash fired after the shutter button has been fully depressed - but before the camera's reflex mirror goes up - E-TTL uses the camera's evaluative metering sensor to analyze and compare ambient light exposure values with the light reflected from the subject by the preflash. This data is used to calculate and store the flash output required for optimum exposure of the main subject (identified by the AIM system), while maintaining a subtle balance between foreground and background. This method provides several extra features such as Flash Exposure Lock (a method of spot metering with flash) and FP flash mode (the ability to use flash at high shutter speeds). E-TTL requires the use of EX-series dedicated Speedlites such as the 550EX, 420EX, 220EX, 270EX, Canon MT-24EX Twin Flash or Canon MR-14EX Ring Flash in combination with a compatible camera.
I also dial in mostly -1 FEC (flash exposure compensation) depending the the background and fine tune from there. When there is no bg or bg is dark, i increase the -FEC (i.e from -1FEC to maybe -1.3 or -1.6, or even -2), and when the bg is bright, i reduce the -FEC, or even dial in +FEC ( i.e -.7, -0.3, 0, +0.3 or more)
For a detailed explanation on the use of FEC (Flash Exposure Compensation), pls refer to this post.