Best is always going to be subjective and really invites debate
I'll start with solid choices that will grow any coral you want and have high bang for your buck- after that, you can research other options that might or might not have better craftsmanship, warranties, spectrum, apps/bluetooth, sleeker designs, customer service, country of origin, etc. and determine which features are and are not important for you. That should help "bookend" your choices.
In terms of T5, the basic setup would be a 4 bulb 24" hydroponic fixture. Replace all lights with ATI/geisman bulbs (your choice of spectrum). The high end version is the ATI sunpower and there are a variety of fixtures in between and special considerations such as hybrid fixtures (T5 +LED).
In terms of LED, the basic setup would be a blackbox LED (e.g. MarsAqua, viaspectra, etc.). The high end version would be the radion G4/G5 and there are a variety of fixtures in between.
*There are other options at both the high/low ends, but I wanted to keep this simple and not muddy the waters with too many choices off the bat- if you have other considerations, I'm sure the community could help pinpoint the exact light that you're looking for. I don't mean to suggest that ATI Sunpower or radion G5s are the reigning cream of the crop- just easy examples of high end fixtures*
