These links should help
Various Light Sources on Colour Checker Cards
Basically as i understand it
MT-G2 for crazy brightness & flood
XM-L, XM-L2 for brightness & flood
XP-G, XP-G2 for brightness & throw
XP-C, XP-E for throw usually in smaller lights
XR-C, XR-E older emitters good in zoomies
Nichia, nice colour or tint
SST-50, SST-90 for brightness & flood
Generally, depending on optics the larger the die or yellow wafer part that you see under the dome, the more floody the LED will be and the more current you can put through it = brighter.
The dome is there to make the light go out in all directions so when you de-dome an LED the light comes out more directly forward. (i think) 