The general consensus seems to be the Ranger wears better, but the Omega is higher quality and more interesting.
I guess that's a nice summary, although the quality gap is small and the "more interesting" is quite subjective. The Ranger has a better bracelet for sure - it was one of the things that got me interested in the watch in the first place (Tudor got on my radar for the BB58, but I didn't like it's bracelet).
I have a Ranger and I've tried the 40mm Railmaster and my opinion is that the Ranger is a better value for the money. (although the difference is not huge - something like 3k EUR vs 4k EUR) Yeah, the RM has a better movement, but other than this and the Omega brand equity I don't see it having any major advantages. Both dials are fairly spartan IMO, but this is something, I actually like. I really dislike the fauxtina used by the RM to make it look older, though - I've never been a fan of faking a vintage appearance. That looks OK on the white dial, but it's pretty obtrusive on the black dial IMO. If I ever get a Railmaster I'd probably go for the version with the denim dial and the white lume markers, because of this.
I know the Ranger is widely hated for its "boring" dial, but I totally love it. That's the one watch I wear almost all the time these days. A very understated and comfortable timepiece. Mine runs fairly accurate - it has lost something like 15 seconds in the past 2 weeks. Despite a bad initial experience (the first Ranger I got was defective and had to replace it), I totally my Ranger and it keeps growing on me every day. But again - I wouldn't mind getting an Omega alongside the Ranger down the road, although I find the AT and the Globemaster a lot more appealing than the Railmaster. Again that's just because I really hate artificial aging, and for all that has been said about the Ranger it doesn't actually use fauxtina. (the lume markers are some light shade of green)
In terms of dimensions/comfort I'd say they are essentially the same. Both fit perfectly my 6.7 inch (17 cm) wrist.