The Space Needle is a 2C Maglite and runs off of 3x123's whereas the Megaclops is a 2D Maglite run off of 6 AA's. The reflectors are the same and the difference in brightness between the two depends on the LS itself. Both are excellent flashlights and I highly recommend them. I personally have a SNII (RB), a Megaclops SE, and whats sort of a SNII/Megaclops HD mix (3x123 in a 2D Mag) which was built by Mr. Bulk.
Which one to buy? IMHO that's a matter of whats more convenient for you. I prefer the HD's over the SE counterparts and which bodysize I like better really depends on the situation. Oh and try to get a UCL from flashlightlens.com if you do purchase one. They really do make a difference.