I think the depression about if Alton Towers is or isn't the UK's number one theme park stems simply from the 2011 developments and offering at the park.
I, myself am feeling incredibly frustrated and disappointed by the current season at the park, and it would seem so too, are the general visiting public - going by the fact that on no visit this season has ride close been extended when I have been on park (indeed, today it was 1/2 hour earlier than had been advertised) and that the queues at the park, aside from one or two occasions, have been really low - today would be a prime example.
It would also be true to say that other parks - namely Drayton Manor and Pleasure Beach Blackpool (both major competition to Alton Towers) have made shrewd investments in the family market this season with big pulling power from a famous IP. That's not to say, of course, that I have any idea if either parks visitor figures are up, although I think Drayton's are for certain (they, of course, have also added Thomas Land in recent years - another great move).
However, there is more than one or two seasons investments to consider when labelling a park "no. 1". Alton Towers still has the most visitors in the UK. Twelve months ago, there would have been no question for most of us on here that it is/was the no. 1. And, let's be honest here - does one season of no investment and increasing prices/upselling etc. suddenly rank Alton below other parks? In my eyes, no it does not. It would, quite honestly, take 4 or 5 years of practically nothing at Alton Towers whilst Blackpool and Drayton (and the others) add things left, right and centre before there would be any shift. Thorpe Park I don't consider ever in with a chance for as long as they only focus on one market as for me, I would like theme parks to cater to all - as I believe this lends itself to a far superior atmosphere. That said, for thrill seekers, Thorpe would already be #1. Chessington is a great family/kids park, but again, stutters due to not being a "for all" theme park. Alton, Drayton, Blackpool, Flamingoland etc. all attempt this.
Blackpool, let us not forget, prior to the addition of Nick Land, had made practically no investment in rides/attractions for several years and, even then, only added a second hand off-the-shelf SLC model of which there are dozens around the world and enthusiasts don't rave about whatsoever. Alton, of late, have added a family coaster, excellent aquarium, half-arsed children's area re-theme, very well themed Splash Battle and other rethemes. I would actually say it is Drayton Manor who seem to be accelerating at the faster level and I, to be frank, relish this. Drayton completely lack a decent rollercoaster - but with their lovely looking hotel, excellent family developments and improvements to staffing - they are sure to be on Alton's radar at the moment.
So, to sum up, there's more to the UK's number one than just one season of ill investment. Alton Towers has been the UK's premier theme park for about 15 years now (prior to that, I would have argued Pleasure Beach boasted overall better rides/attractions) - this is why it consistently has 2.5-3million guests a season, is the only UK park to conduct true nationwide advertising and is the first park on any international enthusiasts lips if they're visiting the UK (well, perhaps not TPR, who we all know, adore the Pleasure Beach for, above all, it's rustic British charm).
Of course, if you applied the question "which is the UK's number one park for effort" then well, it would be a completely different ball game.
One thing's for sure, Alton can't sit on its arse for much longer.