Question:
Where is a perfect place to place the mic infront of a 2 speakered amp?
Answer:
Doesn't matter. I'd pick one speaker, point it towards the middle for more presence, or to the speaker edge for less. You can also experiment with micing in the back of the amp right next to the speaker if there's space.
Answer:
The general placement is usually between the cone and the edge of the speaker somewhere, but generally a bit closer to the edge than the cone. As was mentioned, though, your preference may very. Never right on the edge or right on the center, though...not in my experiences anyway. Once you find it you use tape and mark it.
Answer:
It also depends on if this is live or in the studio. In the studio, I usually put a 57 on one of the speakers somewhere between the middle and edge of the speaker, a 57 on the back of the amp (make sure you reverse the phase!), and a large diaphragm condensor farther back. I usually get pretty good results with it like this.
If we're talking live, put a 57 (preferrably) somewhere in between the middle and edge, like others have already mentioned.
In the end though, its really up to you and how you want it to sound. Experiment. Don't just listen to us. What do we know? Move it around till you get the sound you like with your amp.
Answer:
I'd use a condenser like a Shure SM81 about 3/4 of the way between the cone and edge on the edge side.
A condenser has a little more of a zip on the high end to help cut through the mix.