| depends on what you want. I had a 748r and it is by far the more involving bike than the 998, but as Phil says the 998 is the lazy option.
If you are doing track days or want a bike that is desperate to be ridden hard and enthusiastically go for the 748, if you want to go on longer rides with mates on litre bikes and not come home as tired, the 998 is far easier to live with in terms of grunt, its simply pulls in whatever gear where the 748 requires you to think and react more.
if its the 748 you go for make sure the rockers are done before you buy, other than that not much difference in running costs from my point of view. | 
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