Having just gone through the league and Conference league tables, I'm up to 72 clubs visited, but the number of stadiums is a bit higher with quite a few clubs having built new grounds which complicates things a bit.
I'd say the worst ground visited was Hartlepool (v Albion in the early 1990's), and at the time it was a 3 sided ground (one of the side stands had been demolished) and it was an open terrace behind the goal, and the other 2 stands were just small "sheds".
It was a bit of a desperate place, and we'd arrived late so didn't even have a pre-match pint. Just one of those away days that seemed more of an ordeal than a pleasure.
I spent half the match gazing out at the ships sailing up and down the nearby North Sea coastline.
Best stadium - I used to really like the old St Andrews before it got redeveloped, what I call a "real" football ground, in a dodgy area, plenty of Pubs on the walk from the city centre and a real "edge" about the place.
From one extreme to another, I also like Craven Cottage, again a real traditional football stadium.
Griffin Park at Brentford is another one I really enjoyed visiting with the Albion. Again, a "proper" football stadium, and a Pub on every corner.
I'm not a great one for the modern stadiums, and prefer grounds that are a little bit different as opposed to the symmetrical identikit boring new grounds all over the place, though acknowledge the Emirates as a football ground is exceptionally good (even though you do feel as if you've gatecrashed a Corporate day out in many respects, plus all the daytrippers / touristy types all over the place).