[Edit] Completely rewritten...
I have a Salvo 21w HID, Light Monkey 21w LED, UTD Vision 21w LED (really a 21w Equiv but a 10w I think and it certainly holds its own to a 21w HID in our local waters). I have owned a Hollis 16w LED in the past and liked it alot, too. I always brought my 21w HID for buddy and used the 16w myself, I just really liked the 16w LED better on night dives. For our local diving I have come to prefer the LED variants. None of my LED's are focusable but I don't personally see that as a disadvantage. I've used them on wrecks, caves, low-viz/high-viz local dives, and muck. I have yet to wish I had an HID when I didn't.
For high-wattage LED to HID on team, communication shouldn't be too much of a problem. But if you get a 12w LED in our local conditions when members of your team have brighter lights, then you're beam may get washed out. In that case, we would just put the weakest light in a different position on the team.
It is easier to add E/O connectors to LED lights than HID (HID with ballast in can can't be converted). So I have just two battery packs but different light heads to connect: Light Monkey 21w LED, UTD Vision 21w (equiv) LED (which definately holds its own), 12w Light Monkey LED, UTD Vision 50w video lights (dual 21's), or split between light and drysuit heater, or whatever else can be plugged in. If budget was a concern, you can go the E/O route and upgrade your light heads later as budget and motivation permits.
When we dive together this weekend I'll bring with me a 21w HID and the LED to give you an idea of the differences side-by-side.