I think everyone should have a 6P or similar P60 host. They never become out-dated with new emitter releases, and they are easy to lego and DIY mod too. At $13 (Lighthound) the Solarforce L2 hosts are a no-brainer.
You can just drop in whatever you want... warm tint, cold tint, flood, incan, IMR, RCR123, 18650... Heck with some lego stacking you can even run NiMH cells. The smaller Solarforce L2M will fit 1AA/14500.
Lets not forget Surefire Nitrolon and the streamlight polytac too.
If you want higher end... think Elzetta, Leuphold, SF-C2/M2 and Malkoff devices.
So you got a bunch of Eneloops and are feeling left out of the Surefire fun? Get a 9P or C2, they will fit 2AA NiMH cells with some paper rolled up. Solarforce makes low voltage drop ins for relatively little $$.