We've used all three mvb's you mention. We believe that the MegaR & T-Rex are superior bulbs, though we've received comparable output levels from our SolarGlos (per our Solarmeter). Here's the main difference, in our opinion.
Megas and Rexs output the most UVB - bar none and substantial heat levels (you must be careful with all MVBs, especially the PowerSun which produces mixed reviews). The SolarGlo, though putting out acceptable levels of UVB, seems to be a bit more prone to 'blowing out'. In the last 1.5 years, we've never replaced our Mega or Rex due to blow out - we've replaced 4 SolarGlos (out of 12).
Now, if you look at the cost - Megas and Rexs are $50 shipped, online. SolarGlos are about $35 shipped, online (but we actually were buying them for $25.99 at the local pet store).
That all being said - you get what you pay for. The cheaper price of the SolarGlo is enticing but in the end, you will likely replace it more often than a Mega or Rex, evening out the cost a bit.
In the end, we switched to all Megas, in the enclosures that run mvbs and ReptiSun 10.0s in our CritterCondos. Hope this helps a bit.
Anthony