I feel like all major stations have their pros and cons so might change my v mind about this, but my two contenders would be :
Leeds - very busy for the size of circulation space and years ago my sister was pulled out of the queue to buy tickets in the station (having got off a train from a station with a closed ticket office) by an aggressive member of staff and accused of trying to avoid paying. Come to think of it there was always a massive queue at the internal ticket office too.
Bristol Temple Meads - the platforms themselves and the train shed are fine, but basically everything else isn't (Tbf it's about a year since I used it regularly now though). There were always queues at the ticket machines, the entrance is ridiculously small for a major station, limited retail offering, and the steps down to the tunnel from the entrance feel like an entrance to a public toilet rather than the main access to all the other platforms, and they just get really congested at busy times. They also had a really long queue to buy tickets inside the gate line too, although I never had to use that facility. The trains were also crowded and unreliable to top it all off.
Leeds - very busy for the size of circulation space and years ago my sister was pulled out of the queue to buy tickets in the station (having got off a train from a station with a closed ticket office) by an aggressive member of staff and accused of trying to avoid paying. Come to think of it there was always a massive queue at the internal ticket office too.
Bristol Temple Meads - the platforms themselves and the train shed are fine, but basically everything else isn't (Tbf it's about a year since I used it regularly now though). There were always queues at the ticket machines, the entrance is ridiculously small for a major station, limited retail offering, and the steps down to the tunnel from the entrance feel like an entrance to a public toilet rather than the main access to all the other platforms, and they just get really congested at busy times. They also had a really long queue to buy tickets inside the gate line too, although I never had to use that facility. The trains were also crowded and unreliable to top it all off.