what do you plan to do with the laser? what are your wants for the laser?
best in ultimate portability:
wickedlaser or leadlight
best in overall portability w/ power:
CNI PGLIII (size of a surfire tactical light)
not sure about non portable units w/ cooling...
if youre concern is only playing around, i would really recommend a wickedlaser. theyre lots of fun for and the beam is clearly visible on the higher powered units. if you want your own version of a light saber, PGLIII... youll pay for it though. Im running a group buy on them now if youre interested... theyre anywhere from around $300-$700 depending on what power you get.