Let's see, where do I start? I've got six kingbrite 240w boards. Two are 3500k vegging boards. It's all I use them for. I also have four 240w 3000k + 660nm + uv + ir kingbrite boards. I have those in one of my 5 x 5's. All of my kingbrite boards work well and grow great bud.
I also have the Grower's Choice ROI-E720. It has 660nm red, I believe IR but no UV. I have $1000.00 in this light. It's currently in use in my other 5 x 5. I prefer this light over the kingbrite boards. The quantum boards don't fill the space as well as the E720. I have to run 960w of quantum boards to get the same results. The Kingbrite Quantum boards are good boards, but the E720 is clearly better.
HLG Scorpion Diablo is not an ordinary quantum board. If you were to look at the diode counts between a kingbrite board and the
HLG Scorpion Diablo, you'll see it has about half as many diodes as the
HLG board. This means that the Kingbrite board is driven harder and it still doesn't reach the numbers of the Scorpion Diablo. The higher diode count allows
HLG to drive them softer which is what makes them so efficient in comparison.
When I outfitted my second 5 x 5, my choices were the Diablo and the E720. I chose the E720 because it was $400 cheaper, was a bit higher in wattage, and according to the salesperson I bought it from ... runs cooler than the
HLG board. Most likely I would have been happy with the other one too, but I really like my E720.
With that said, buy the best light your budget can afford. Just keep in mind what is best isn't always the most expensive.