The question of what's "best" for your space has a few variables. The first is: What is leading you to LED? Energy efficiency? Heat reduction? Low-cost fixtures found on eBay? IMO, the only productive use cases are energy efficiency (and lower electrical use), but this requires a significant up-front expense. About $800 more for a 4x4 tent than the inexpensive eBay fixtures. If you grow in a short space, some of the inexpensive eBay fixtures (the ones with 3w diodes mounted on white backboards which allow minimal distance between the fixture and canopy) are a legitimate choice. But, you can do about the same thing with T5HO. In any other circumstance (taller space, limited budget), CMH is typically recommended.
Regarding LED "lightbulbs." CaptainMorgan did a thread growing with Cree A19s sold at Home Depot.
I distilled everything I learned from that into this article. Cree also makes a more powerful/concentrated 18w PAR38 flood/spot.
I made a fixture to hold 5 of those as top-lighting for taller plants (in a taller space). I haven't grown a plant with it yet. It was just an idea I had after thinking about the various ways to use the A19 bulbs.
These bulbs are slightly more efficient than T5HO (which is 92 lumens per watt. By comparison, CFL is in the 65-75 range.). The Cree A19s and PAR38s are in the 90-100 range. There are "lightbulbs" using SMD5730 diodes that are supposed to be in the 105-115 range. But, these may suffer from the same supply chain problems that plague Chinese import Epi-whatever fixtures. (After hearing about them, one person ordered a couple but they're very dim, draw only 3w instead of 15w. I'm waiting to receive my order.). Either way, there definitely will be more efficient "lightbulbs" soon.