There is an aweful lot of differences between those 3 cameras, not the least of which is the VX runs about $2200, the FX $3000, and the XL2 about $4000.

Advantages to the XL2- Native 16:9 chips, 24fps, xlr audio.

Advantages to FX1- HD, native 16:9 chips.

Advantage to VX- Best low light camcorder under $4000.

Do you want to shoot in SD or HD??
Do you want to shoot in 16:9??

For the audio, you can get XLR adapters. You wouldn't want to use the onboard mic for any of them.