Well, if I HAD to play a factory guitar ... it all depends on the individual guitar. And also, what year was it built.
Because you see, if I could have a guitar from the 1930's, I'd probably go with a Gibson. The `30's Gibsons always seem to have something to them. If you get a great 1930's Martin, they are damn fine guitars, but I've also played some really lousy ones. But a 1930's Gibson - I've never seen one I didn't DESPERATLY want to own. The usually need a ton of work. We have one old friend who has a early `30's Jumbo - more or less a J-45 - that has such a small bridge that it needs to be reglued every few years; and another old friend of ours has one on which the scale length was so badly executed in the factory that we had to replace the fingerboard (it is a beat to shit players guitar, and putting on the new fingerboard had little effect on the market value of the instrument, but made it into a very, VERY nice players guitar). Unlike the current ones, those old Gibsons were consistent as hell, and absolutely fantastic.
But if it was a 1950's or 1960's guitar, it would have to be a Martin. Sure, they made some guitars which were better in the `30's and `40's, but they are so hit or miss. In the `50's and `60's, they were making fantastic guitars, were as Gibson was starting to use those awful plastic bridges (the worst idea Gibson every had, followed closely by those adjustable ceramic saddles).
In the seventies, the top prize probably goes to Guild. That was there golden age, hands down. Gibson was spiraling down the path of mediocrity, and Martin was making so many damn guitars that it took them ten years to notice that they were putting the bridges IN THE WRONG PLACE!!!!!!! Guild, on the other had, was putting out some really fine stuff, and some of the nicest production 12-strings you will EVER play, hands down.
The eighties is a bit of a waste land for acoustic guitars. Martin went from building over 19,000 guitars in 1972 to just about 3,000 in 1982. (Though they did it without firing anyone, which I think is pretty cool of them). Gibson in the eighties, well, the less said the better. Taylor was just starting to get rolling, and Guild was pretty iffy. Still making nice guitars, but past the golden era.
Thank god for Eric Clapton.
The Eric Clapton: Unplugged episode was a BIG FUCKING DEAL in the acoustic guitar world. The guys who managed to stay in business until that happened were rewarded for their tenacity (or some would say stubbornness). Most of the acoustic guitar store owners spent the early eighties running up credit card debts just to stay alive, or they went out of business. I have one friend who had a business consultant tell him that if he didn't close his store, he would be bankrupt within the year (but he just didn't know what else to do, and now his store is one of the most important acoustic music stores in the world).
But then Eric happened. (Big sigh of relief as the heart monitor on Martin Guitars starts to flutter again)
In the nineties, it became possible to get a great guitar from just about anyone, and that continues until today.
So, if I was looking for a NEW guitar today, it would be about price range. In the under $1,000 range, you will not find a better made or sounding guitar than
a Martin D-15 (or a OOO-15 or a OM-15, or really any of the style -15 guitars). I can all but guaranty that if I had that little to spend, that is what I would get. Above that, I wouldn't even look at the name on the headstock. I'd just go into a great store (Gryphon Music in Palo Alto, The Podium in Minneapolis, Gruhn's in Nashville, etc.), put on a blindfold, and have the sales staff hand me guitars until I found The One. There are just too damn many nicely made guitars out there, and I can't see any reason to pick on anything but the purely subjective terms of what I like.
Which is, I suppose, a really long non-answer to a fairly simple question.
But the real answer is my favorite acoustic guitars are made by my dad, and what kind of an answer is that when I won't even tell you his name.
Light
"Cowards can never be moral."
M.K. Gandhi