Ive used COBs for my very first grow. Then, I switched to boards. I love both of them.
With cobs, I get a good concentrated light source, which means good things for my rather open area (Not tent). Less light loss. Best part it, there are lenses to help you focus from 120 to 90 to even 80 degrees. Must be more that I don't know. My 90 degree lenses gives me excellent results. Large dense buds. I use 6×65W 3500K plus 2×50W Blurple full spectrum during flower. Yes, there are good full spectrum cobs out there and they work great as red/blue supplement during flower. Or, you can spend more to get CREE red/blue supplement cobs to supplement your white light.
Cons of cobs imo are that most of them are not dimmable. I find that dimming them is rather useful but not as important as boards. I won't buy an undimmable board but will buy an undimmable cob. With cobs, i find it less easy to get an even spread of light. Since they are concentrated as hell, center gets higher ppfd. Two cobs sharing center beam can burn plants. I prefer the more even spread of boards in this case. Watt for watt, lumen for lumen, boards still kinda makes more sense.
With boards, I love the DIY aspect of it where you can cater to your own conditions. Even spread, best efficiency at the moment. Add more boards, strips, bars whatever in different color temps or even add mono color diodes to complete the spectrum much easier and cheaper than cobs. If you already have a main light and wish to add a certain spectrum to your setup, a big concern is spread. Say you wanna add Royal Blue. With cobs, you may need quite a few to spread it evenly throughout your area. With strips, bars, boards, its much easier and cheaper. Dimming helps me save power the first month which is quite significant as I use as little as 25% only. Each board, strip, bar can be controlled individually to create the spectrum you want. They also look brighter to the human eye.
CMH has spectrum that is lacking in LEDs. Of particular mention is the Blue and UV spectrum. These help grow buds that are both potent and resinous. I am currently supplementing short periods of MH lights daily to my flowering girls. Plan is to give a more complete spectrum along with UVB to increase potency.
So as you can see, they are all great in their own way. Just see which one suits you best! Budget, goals etc.
