Anything is expensive if you can't afford it!
Martin guitars, like any other, will vary in perceived quality of tone; but that is so subjective as to be almost meaningless.
I have owned close on a dozen Martins and currently own one, a 0000-36 Custom and three Gibsons; Advanced Jumbo, SJ 200 and J185 Koa Custom.
They were all expensive but what I'm paying for is premium tonewoods, great build quality and superb tone. It takes a long time to find really great sounding examples but, if you take your time looking, they are out there and when you find THE one the expense is easily justified.
I'm also paying for intangibles; heritage, ownership of a bit of guitar building history and pride of ownership.
If you think Martins are expensive then take a look at Jeff Traugott's creations-they start at $26,000. Martin prices pale into insignificance...
As to what's the best guitar; it only exists in the ears and hands of the buyer irrespective of the name on the headstock.
In 1969 my lowly Yamaha FG 180 was the best I could afford and at £40.90p was a lot of pocket money for a 16 year old kid.
It's all relative and it's all good.