Robbie Keane was the best player in the last 2 decades.
Dublin made a greater contribution over a longer period but that was not the question. He was not as good as Keane.
Huckerby was summed up by strachen perfectly , 1 week world beater, the next week carpet beater, had ability just lacking a bit up stairs, holds the unwanted record of the most offsides in a season, top bloke though had a proper drink with him and whelan in the red lion one sunday, top craic.Ndlovu was class, but Huckerby by far the better player for me. Huckerby also played at the top for a longer period with several clubs in a top flight full of star foreigners. You only have to look at how Norwich City fans worship Huckerby to understand what a great player he was.
As for opening question, Dublin or Keane for me. Heart says Quinn, but great as he was, would he have scored a hat-trick at Arsenal on the opening day 10 years after he did? The game moved on very quickly through the 90s. Players like Ndlovu and Quinn who shone at the beginning of the decade would not have stood out so much by the end of it.