When it comes to products there is no "best", its all 100% subjective!
To me personally , the best mustangs are from 66 to 70 CBS mustangs. (I have a 1966) They have a bigger headstock than the pre CBS 64 headstock (which I hate) plus the models between them years com in the 3 patriotic colors (pre CBS did the three colors too ) and it also includes the competition mustangs. The quality of 66-70 mustangs is no less than the pre CBS 64 in my experience but pre CBS is more desirable for reasons I couldn't give a phuck about.
Today, the best mustang for your money is a Japanese 65 or 69 reissue. they are cheap, almost 100% vintage correct and sound great.
If you want vintage, the best value for money is probably a 70's mustang or anything post 65-66 at least anyways. 64's sell for more quite a bit more.
Ebay always has bargains to be got but you need to do some research first or you may end up with a dud,expensive refinish job or something else entirely.
Vintage mustang pickups,much like the modern Japanese counterpart, are very low output and a little thin sounding for rock music. They sound great clean but aren't much good for anything else. They are only around 5.5k, that's pretty damn low for a single coil. The Japanese Mustang pickups sound pretty vintage correct also, like a Vintage mustang pickup would have sounded all those years ago.
I replaced both the pickups on my 66, a DiMarzio DP218 in the bridge and a Seymour Duncan a Jaguar antiquity in the neck. IMO, ALL mustang pickups need replacing with something hotter...for the music I play they do anyways. SD also makes Mustang Antiquity pickups if you're after than vintage sound. You seriously cant hear a difference between a real vintage pickup and a SD Antiquity, they sound identical.
A mustang with a 14 plus Kohm humbucker in the bridge is one gutsy guitar, its a very powerful sounding instrument!
Contrary to popular belief, the mustang vibrato can be set up perfectly and will ALWAYS stay in tune, even with excessive vibrato usage. Most people just don't know how to set them up correctly.
Mustangs also have 250k pots which can sound a little dull, they sound better with either 375k or 500k pots. It gives it more output, clarity and a fuller sound.
The phase reversal on mustangs sounds nice IMO, Fender went about it with the switches a bit ass up because there's too many switching combinations but only 4 sounds (bridge/neck/both/both phase) you can get out of a mustang.
Some Mustang models have arm/belly contours and some (the earliest ones) don't, I like both TBH, it doesn't bother me. But ALL Mustangs have an offset waist.
If you buy Japanese you can get 2nd hand and its cheaper still and you will end up with a great guitar, if you buy American you will pay more.
Fender Japan makes better Mustangs than they do Jaguars/Jazzmasters. They are at least as good as Fender USA AVRI series Jaguars/Jazzmasters in the stock condition.
There's this page you can read and learn a fair bit about Mustangs, its a good resource for info: LINK