omnimic just works.
REW has hassles.
I've used both, I've seen both used multiple times.
You can pull the omnimic from my cold dead fingers. I'll give you REW for the price I paid for it.
I don't want to be fiddling around with setup endlessly, and try to iron out weird random problems all the time. I want to pull my mic out, take measurement, and move on. The real-time measement with omnimic is invaluable. I can go to any room with any Windows PC, and take an accurate SPL calibrated measurement in less than a minute. If they have the capability to play a CD or a mp3/wav file (what home theater doesn't?) - that's all I need.
Home Theater Shack reached out to me at one point through PM and asked if I'd consider becoming an official subwoofer reviewer there, but they had a couple conditions - neither of which I was comfortable with. One was to drop Omnimic and start using REW, because REW is promoted there. I'm glad they make a great tool, and it's free, but like I said, I've played with both, and I'm going to pull out the easier to use, hassle free tool every time.
Dessertdome used to be a big proponent of REW, he relatively recently bought an omnimic, and conceded that for ease of use and immediate startup time the omnimic has his vote, and it's what he uses most of the time now, even though he still knows the ins and outs of REW. I know there are guys that love their REW. I'm happy for them, and I'm happy there is a free software option and I truly applaud the design team and ongoing improvement efforts and the fact Home Theater Shack keeps it free. I just like omnimic better for my casual use. The all in one package, with realtime sweeps so you can see exactly on the graph what that 2% angle to-in or physical replacement of the speaker 2" to the left does to the frequency response at the MLP. It's truly so easy a cave man could do it.
As to optimizing your room to the nth degree with treatments, frankly I'm just not that into that. I've been in many rooms at many avsforum home theaters, and room optimization/speaker optimazation is easy to do in a major way without all that expense that makes it a tad bit better. Use the REW or Omnimic tool to optimize initial physical placements - let your AVR's auto EQ take over from there. I had a super live room in my last theater room and I loved it. I have a more dead room now, and I love it. I don't get too uptight about the details. I'd be happy in either type of room again -- and I had lots of compliments about both rooms. Just optimize the subwoofer placement to start with as flat of an EQ as possible in the MLP, and likewise optimize the speaker physical placement and toe them in to your preference and K. I. S. S.
Use some common principles that seem to work well. Deaden the front wall, use carpet where you can, if you have a drop ceiling install sound aborbing panels an pink fluffy above them, if not install a couple absorption panels like
did. Play with absorption panels on the side wall if you like, or buy speakers that have more limited dispersion horizontally (constant directivity type for instance) and toe the L and R in a bit. Don't automatically assume absorbion panels at the first reflection point is the right thing to do because some people say it is. Maybe contra-lateral panels are what you need? Maybe like me you'll find you don't even need panels at first or contra-lateral positions and you're happy with the sound as is. I ended up hanging some 3" studio foam in kind of a strange, unexpected place on the wall behind my computer monitor because I was hearing a bit of a slap echo originating strongly from there. It wasn't really a measured thing. It was an audible fix.
Sure, my room could probably be a bit more optimized with a proper acoustic engineer at the helm - but IMO, I'm pretty happy with the results as is - in just playing around with stuff and using these basic principles. My room, IMO, easily bests any commercial cinema I've ever visited except the newest AMC Prime (premiere flagship theater), and my bass is better than the prime, so I'm really only giving up a little bit to the main speakers (JBL line arrays) the seats, (electric recliners - super comfy) and laser projectors (which are phenomenal). All of which if purchased and installed would probably 10x + over increase the cost I've spent on my room - for no where near that level of appreciation over what I have.
If you want a recommendation on a good professional acoustic design person - dlbeck used Niles from Acoustic Fontier, and his theater is the best I've ever visited --- so I'd start there. dlbeck has very solid recommendations for Niles. Niles planned absorption, diffraction, and reflection treatments down to 1/4" IIRC in dlbecks room. And obviously it worked... I'm just not at that level, not really sure I need to be at that level for my personal financial and interest level.