OK lets say - best of the:

1950's
1960's
1970's
1980's
1990's

And today

I'd nominate mark Rocco who was around for three decades but was most prominent in the 1980s so I'd go for that one. As for reasons - how many do you need - the man was pure excitement and way ahead of his time.
Kendo nagasaki is a similar case whereby he covered a number of eras but you cannot have a hall of fame without him

Les Kellet - A great technician and a brilliant comedic wrestler. He didn't have to do silly spots with his ar$e hanging out or fall face first onto the mat to get laughs. Unlike certain wrestlers (*cough* Flair *cough*)

1950s - Bert Assarati - the best British heavyweight of his generation. Amongst the very best in the world in the 50s and before.

1960s - George Kidd - World lightweight champion for many years. I would like about 6 votes for the 60s (my era) but can't do a list of the best without including the man with wrestling skills, especially counter moves, that were better than anyone else I have seen in my 5 and a bit decades of watching pro-wrestling.

1970s - Kendo Negasaki - a kind of X factior of star quality. If he was on the bill it was guarenteed excitement. An amazing ability to wind-up the crowd, excellent mobility for a big guy,and moves that for a long period only he could execute.

1980s - Tony Sinclair - By the 80s grew into an excellent world heavyweight champion from being a very good wrestler at lighter weights when a young man. Has Contributed to the game as a wrestler, referee, promoter, coach and by postings on this website. His done the lot.

1990s - Dynamite Kidd Tommy Billington - Tommy was dynamic, tough, fast, highly skilled and proved himself around the world. Had he not been seriously injured he would still be active today and a big star.

2000+ - Steve (William) Regal - I am going for Steve because he knows how to wrestle (ask Goldberg), is strong and tough, and so far as British wrestlers go his fame is second to none in the current era. (Sorry Doug and Robbie)

1990s - Dynamite Kidd Tommy Billington - Tommy was dynamic, tough, fast, highly skilled and proved himself around the world. Had he not been seriously injured he would still be active today and a big star.
Well as a bit of a Dynamite Kid (only one D by the way) fan I have to say that his involvement in British wrestling was almost entirely witihin the 1970's, apart from a few "guest" appearances on the British scene in the early '80's. His major US and international successes were in the 1980's. I can't agree with him being classed as a 1990's star in any arena.

In era order
1960s - Les kellet, mick Mcmanus, Jackie Pallo, george Kidd
1970s - Tony st Clair, Wayne Bridges, Johnny Saint, Jim Breaks, Alan dennison
1980s (my era and the highlight of TV wrestling)
mark Rocco
Kendo nagasaki
Dave Finlay
Marty Jones
Alan kilby
and I suppose you have to include Big daddy and Haystacks