Anderton
The best compressor is a singer who has good mic technique - backs off when screaming, gets close on the intimate parts, etc.
Then you don't need a compressor going in, and can get consistent levels that work well with compression during mixdown. The PC2A is a great vocal compressor for mixing.
I definitely agree with this comment.
I read through a few of the comments above where people are relying on hardware to do their work for them. While that is ok.... I wonder if it's the best way.
In my rig, I have a Saffire interface by Focusrite. It has a built in FX DSP in it's control panel. I did set it up to run a very light compression on all the incoming signals..... guitar and mic. Nothing over the top. I have to pay attention to the mic technique I use or it can easily clip on the peaks. As a result, I have learned better mic techniques and every now and them I have to redo a part that "gets away from me". I do not often have outside singers in my humble studio but when I do I have learned to pay attention to the waves and instruct the singers on mic technique and punch in when they clip.
As a result of this I get extremely consistent vocal takes which require very little compression to make them fit and set right in the mixes.
I do not rely on the hardware and the software alone.... it is a combination, relying mostly on good recording techniques up front.