I have a lot of traditional 9mm pistols... if I wanted just 1, I would look at the following:
Top tier (to me):
Sig P226
Beretta 92
CZ 75
This were considered the best production guns, and they are all still being made. Older versions are around that can be had for good prices, under $300 for CZ and Beretta, I've found 1 beat up Sig for not much over $300 (and bought it).
Potential drawbacks to the older guns: things are just a little different vs current production.
CZ- new production mags don't fit in pre B's for the most part, except the 18 rd SP01 mags. They fit.
Beretta- the 92s has a heel mag release, and while new mags fit, they might not have the slot in the correct place. However, Taurus mags also might have that slot, and if they do, they also fit.
Sig- biggest con with these are they tend to cost more than the others, and they aren't necessarily any better than a good CZ or Beretta. If you like a safety, they don't have one.
Next tier- S&W 39/59 series, 1st through 3rd Gen.
Great guns, particularly the 39 versions and the 3rd Gen, all versions. Biggest con- no further current production, and parts (if needed) are dwindling.
These are very good guns, on par with the above guns, no matter what anyone says.