Have used Vltor MUR upper . This is a good forged upper ( original ones were billet ) if you want something different
The Vis is again pretty cool if you want something different. If having a continuous top rail is important for you then have at it. Not much other choices readily available. The LMT MRP comes to mind
Quite frankly I does not bother me that you need to buy their LMT barrels for the MRP. People get all geeked because they see the cost of the LMT barrel. Keep in mind that their barrels should not be compared to "utility grade" barrels. The 10.5 MRP I have is made on a Rock Creek blank
I have DD Lite, KAC FF , URX, etc and I never seem to have an issue mounting optics because its not a continuous rail...even with magnifier etc. The only time it becomes an issue is traditional rifle scope where the ring would bridge the gap. Having said that, that is what the Larue / AMD scope mount takes care off
For the record, the VIS is a great upper and it does not matter its not a true monolitic , like the MRP. It is salt dip brazed from two pieces...useless trivia for the day
See pic below, and you can see the parting line ( top receiver )