I've built the Airfix and Revell (more of the latter than the former) and even though it is a clunky kit, needs work and is getting harder to find, I still prefer the Revell offering.
As for the nose RCS on the Revell kit, there are two possibilities. As has been mentioned, if you're modeling the Orbiter sitting on the pad, it's no big deal because the RCS ports are protected from rain by plastic covers that get blown out when the RCS are fired.
What I've done for my on-orbit shuttles, though, is back the RCS area with layers of sheet plastic or Miliput and then drill out the RCS housings. It's a relatively simple task.
First, before you assemble the fuselage, use diagrams to figure out where the side RCS ports are on each side and mark them. Then, using a few small pieces of thick sheet styrene, build up the area on the inside of the fuselage. Clamp it as best you can and let it dry awhile. Or, build up the area with Miliput. Once everything is solid and dry, you can drill out the RCS ports; make sure you angle the two oval-shaped primary thrusters (konwn technically as the -Z F3D and F1D on the port, and the F4D and F2D on the starboard).
Once you're satisfied with those, assemble the fuselage halves but leave off the payload bay doors and the forward payload bay bulkhead and windows. Determine where the upper three +Z primary thrusters (they're the round ones) and where the three -X primary thrusters (They're the forward-firing oval-shaped ones) go and back that area with Miliput. I've found it hard to get layers of sheet plastic to conform to the shape of the nose, but I suppose if you had the right clamps, you could do it without a problem.
Once the backing is dry, drill out those thrusters and file and sand to the proper shape. When you're done with that, go ahead and put the model together however you want.
I used the Cutting Edge decals on my latest
Columbia, so to make sure my RCS locations would agree with the decals, I photocopied the decals and then cut out the appropriate sections from the photocopy and taped it to the model to determine the locations. It worked just fine.