VHO is very good in my opinion, they are awesome when ran off of Ice Cap ballasts. T5s are great too (though the technology in regards to our hobby is pretty new) Power Compacts are an ok option, but do generate a lot of heat (compared to other fluorescent bulb types) and end up having a shorter life span when compared to VHO or T5. Hot fluorescent bulbs = shifting/degraded light output, power compacts in my opinion are only ok to use when ran by an Ice Cap ballast which does increase the longevity of the bulbs.