You know the problem when making all time sides is which part of a player's career are you taking. People tend to take what is convenient for them. Imran was a devastating bowler for the first part of his career (barring the very early bit) and a useful lower order batsman. Towards the latter part of his career his bowling declined but he started batting more cautiously and as captain took some charge of the lower middle order. Thus when people chose Imran as an all time great all rounder one has to take it with a pinch of salt for we tend to take his career ending figures and then 'spread' them evenly across his entire career although this wasn't how his career panned out.
I think if Imran is to be assessed at his best (as it should be for all greats) then his greatest period as a cricketer was when he was at his peak as a bowler because once his bowling declined he remained a very good cricketer but wasn't a 'great' one any more.
Botham on the other hand, during the first half of his career was a world class all rounder - a devastating batsman and a wonderful new ball bowler and one of the finest all round fielders we have seen. Its rare to see such a period (of great batting and bowling skills) coincide amongst most all rounders. Even Miller's batting flowered later although even in his best bowling times he was a much better batsman than Imran was during his peak as a bowler.
Same with Wilfred Rhodes and even to an extent with Faulkner.
Another misconception people have about Botham is on account of his speed of scoring and his six hitting. I am amazed that this causes people to consider him a 'slogger' for Botham had one of the best techniques you could imagine. His grip, stance and stroke play were almost copybook its just that he was a very aggressive stroke player and his driving was devastatingly powerful. If it did not come so easily to him and if he took it a bit more seriously one would have seen him make massive scores for he was an amazing batsman at his peak. Imagine Sehwag, add both inches and muscle to him and make him play even straighter and off both feet and you get Botham.
Just look at his feet and head position, the follow through and the balance in each of these photographs.
Backfoot drive
Hook : keeping it down
Hook for six
Inside out drive
Off Drive
On Drive
Hook from off stump
Square Cut
These are the strokes of a top order batsman. He just happened to score very fast and was flamboyant in his attitude and would probably laugh after getting out and made more enemies than friends.