Two very different places. You need to work out how much travelling is required between the two, believe it or not, there are not that many flights per day DXB-RUH, and during summer peak season, it's hard to get a seat.

I'd suggest getting a base in Dubai, simply as there is more for a single man to do there. In Riyadh, living options for single guys are limited. Then I'd pick somewhere near to Dubai airport, as you don't want to spend half your life in traffic commuting back and forth from the airport, of course, depends where the offices are in both cities.

I have a number of colleagues in Riyadh.. PM me and I'll put you in touch with them directly.