More of a poll than a debate as I know this is a common topic.
My vote goes for Tendulkar. His away record; longevity, his record against arguably the best team ever assembled Australia; the quality of bowlers he faced through the majority of his career - compared to the bowling attacks of today and in previous periods.
Obviously could list more but Im on a break at work ! (Just realised I listed Hutton twice not sure how to change it to Headly)