Good thing about Lukaku is, he always makes the difference (be it with a goal or assist) when his side is drawing a match. His all-round game isn't up to the standard required of a top striker, but he's still very young and will likely improve. He's already a good striker though, and is going to be amongst the best strikers in the league IMO. However, I'm not yet sure he'll develop into an elite striker. I dunno, maybe I'm spoilt, but I'd like to see a (potential) top 5 striker leading the line for us again.
Balotelli's different, he is an elite talent IMO, there's no doubt in my mind he'll develop into an elite striker if he fulfils his talent. There are huge question marks about his attitude and application though, spending huge sums of money on him is a very big risk. Would I take the risk? Yes, unless we have a realistic chance of signing Costa or Cavani (don't rate him as much as most people do, but he's still a top striker).
The appealing thing about Balotelli despite the huge risks involved is, he's a set piece specialist and we desperately need one. Not only is he very dangerous from direct free-kicks, his delivery from corners or indirect free kicks is top quality. His delivery from set pieces was crucial to Inter winning the league when he 1st burst on to the scene at 17/18.