I'm a firm believer of all three techniques used together.
To sound "comerical these days, you almost always have to use combined vocal takes.....that being said.
For a lead vocal, I will normally track with some light compression, somewhere around 2:1 shooting for around 3-5 db of gain reduction. Something to keep things level.
I dig the Waves C4 comp plugin for each vocal track, It'll allow you to control 4 specific ranges of the voice, work well to thicken the low end and
the desser in there is nice too. the 300hz to 3khz range i normally shoot for another 2-4db of gain reduction(depending on the mix)
I'll also through a peek limiter on my vocal buss just to grab anything going crazy, set that for 1 db of gain reduction.
I'll also "tune" my vocals in Melodyne and add or remove some amplitude to specific words or parts of words.
Thirdly, I will do fader automation for more dynamic parts(intro, bridge, outro)
Compressor(in and out of the box) add characteristcs that amplitude adjustment and automation don't. 2nd and 3rd harmonics, bringing up the "breaths" taiming pops, transformers, tubes, hot plate voltage, add alot.
I'll my mixes to sound "commercial" I want my mixes to sound like "the killers, fall out boy, butch walker, pink, paramore"
that's how the industry is going these days.....if you wanna make cash