ok, I would propose that the best ever is in this list
Barnes
O'Reilly
Lillee
Marshall
Holding
Ambrose
Imran Khan
Hadlee
Akram
Murali
Warne
Unlucky to miss out, but I think justified are
Garner - generally the most under-rated of the west indians but I think he is generally considered behind the three already listed
Grimmett - I think O'reilly was generally accepted as the superior pre-warne spinner
Waqar - can't be considered as Akram his opening bowling partner is considered the superior.
Mcgrath - great record but there isn't many aussies who would pick him as the greatest fast bowler even australia has produced. Walsh is in the same boat, though unlike mcgrath who has only lillee ahead of him Walsh has about 6 or 7 team mates ahead.
Indian spin quartet - lacked a stand out and I doubt anyone would put them ahead of murali or warne.
all english bowlers were mucked about a bit and none stood out for a signifcant time.
Kumble - great player, but playing alongside murali and warne makes it easy to discount him as the greatets spinner ever as he was not the greatest spinner of even his own era.
Of the ones I've listed
I would say Barnes (on ground of playing on stupid wickets and in days when the game was in it's infancy) and O'reilly (i think it's safe to say the best spinner ever is one of murali and warne) can be taken out
leaving us with
Lillee
Marshall
Holding
Ambrose
Imran Khan
Hadlee
Akram
Murali
Warne
can't really make a clear case for any of those above the others. Lillee is maybe the most precariously placed but even he has his trumpeters. Hadlees determination and discipline, Imrans inspiration, charisma and record, Holdings Action and speed, Ambroses menace, Marshalls stats, skill and longevity in a team where fast bowling competition was fierce as possible, Akrams artistry and pure talent, warnes intelligence, charisma and match winning ability, murali's sheer turn and skill, his record and that he took a minnow up to competing with the best teams almost single handedly.
I don't think anyone else can get into that shortlist, but the two I took out I suppose could end up going back in.