Magnum PI
Private Detective
I just top Magnum with 142 grounds watching Southend United (does not include any friendlies).
Since going to my first away game back in the day, I have missed the opportunity of adding 6 more, namely Barrow, Wealdstone, Manchester City (Maine Road), Newcastle United, Wigan (DW Stadium), and Bolton (Macron Stadium). The Man City and Wealdstone grounds have both now gone, but I hope to notch the other 4 at some point, plus the other 9 grounds we have yet to play in the current 92 (Magnum missed out the London Stadium).
Less said about that anomaly the better... When they are back in lower reaches of Championship with 10,000 fans in it, maybe they will try and get a free ride at Orient's ex-league stadium :)