as far as quality and efficiency of light both cobs and the individual diode boards are similar. Both can get you there and have their advantages and disadvantages. currently the best models of both are right there at the top in terms of performance in usable light per watt. Either will be substantially better than any HID youve used in the past, hard to go wrong, even the Crees are great chips but as some people said above, they just cost more (right now) so people ahve moved away from them. People are still throwing down amazing grows with 2 and 3 year old cob tech like cree 3050/3070, vero 29 gen 6, citizen clu046, etc. LEDs have a really long life (10 yrs+ at the way we run them soft), and the older cobs dont really become 'obsolete' because newer models are generally only 5-10% more efficient year over year and just about any of them could be run at current efficiency standards just by cutting current in half.Or if you go the cob route later on you have an easy upgrade because chips are relatively cheap and falling all the time, and heat management and good drivers are a wise long-term investment (current top-shelf drivers are 93-96% efficient with little room for improvement - people liek the Mean Well drivers because they are pretty bombproof, super efficent, 7 year warranty, and come in all differnt sizes and options- for about $0.25/watt - a true bargain)
At any given time one chip mfr could be delivering better value than another. Currently as far as cobs citizen vero and luminus are all near the tiop in terms of value, DIY with respectable efficiency under $1/watt. Prebuilts probably $1.50/watt. as far as discrete chips samsung S561C are some of the best but manufacturers are fighting tooth and nail to eek out more efficiencyat lower costs- a race we all win in the end.
if buying a prebuilt fixture or a board assembly its best to buy from a mfr who can provide actual photometric data for their assembly, usually expressed in umol/J. if that doesnt make sense feel free to ask.