The answer depends on what you're using the light for: cheking on the classic "bump-in-the-night" noises or leaving the light on for extended periods.
For the "bump-in-the-night" role, I'd consider the M6. It's very bright, very small, and lights up at full brightness as soon as you turn it on. Disadvantages? It's expensive to run. The M6 costs at least $18/hour to run on high (it consumes 6 CR123 batteries every 20 minutes, at $1/battery). That said, if you're just using it intermittently, even your first six batteries will last you a while, and it should work fine for home protection.
As for HIDs...
I'd definitely consider one if you're just going to be turning on your light and then keeping it on for a while. As wasblinded mentioned, HIDs take a while to ramp up to full brightness - anywhere from 5-25 seconds (figure ~10 seconds on average). For the "bump-in-the-night" noises, you want something that lights up immediately, so HIDs aren't such a good mix. However, if you'll be using your light for extended periods, the HIDs are more efficient and last longer. Their beam also extends pretty far, and is a beautiful shade of white. =)
FYI, some CPFers are now making rechargeable solutions for the M6. They appear to be very well received. However, the $200 cost of the rechargeable option means that you're spending roughly $550 on the M6. Mini-HIDs can be purchased on CPF for about $250; with charger and batteries, it ends up costing you about $300 - or roughly half the price of the M6. (Just figured I'd throw this in, in case cost was a factor!)
One final HID option is the X990. It's got incredible output and throw, and is available for about $300 with two rechargeable batteries. However, it's also big and heavy - far less portable than either the M6 or mini-HID!
In any case, the M6 and HIDs are all great lights - you'll be happy with whatever you get!