Zombie Thread Alert! lol...
"Best?" I suppose "best" means different things to different people; How it looks on a shelf, ease of reading, quality of paper/print/binding, mobility, rarity, value, etc. So it really depends on what's best for your personal needs. One nice problem to have is that you certainly don't have a lack of choices these days. There are A TON of versions to pick from.
I own several various editions of Hobbit/LOTR ranging from paperback beaters from the 60s to a few of the higher-end releases. Though my choice for "best" may not be the nicest, rarest, oldest, etc., my current personal choice of "best" combines an average of all my listed criteria into 1 choice for a boxset.
And though this may be a case of recency bias on my part, I can't help but to absolutely love the recently release illustrated box-set by Harper Collins that features the paintings of Alan Lee. (I don't think Houghton Mifflin, the U.S. distributor, has released this yet, but you can find the Harper Collins version easily on-line.)
Example photo, not my copy
This new set contains all of the art from the massive Centenary Edition boxset w/Hobbit from 2000 (pre-Jackson's movies, btw), plus newer paintings done since then. (I love that big version, which has been a favorite for the past 20 years, but frankly it's just an easier story to read when the books are divided up instead of wielding one giant book around.
Example photo, not my copy
There are several online reviews out there and I encourage you to go check 'em out. Also these latest editions look great on the shelf next to the illustrated versions of the Sim, the (brand new) illustrated version of Unfinished Tales, and the 3 Great Tales Books (Children of Hurin, Beren & Luthien, and The Fall of Gondolin).
Happy Reading!