I have the Just Right Carbine in 9 mm and love it. But to answer your question you have to answer some. What do you plan to do with the carbine? What is your experience? Does you have any requirements such as using Glock mags? How easy is the weapon to strip and clean? Do you want a breakdown or fixed model?
Once you answer these questions yourself then you can look at some products. I purchased mine back in November > It does not come with sights so I bought Iron sights and a Red Dot.
Also watch some videos on the products available

PSA sells great products. I have yet to get a 9mm, but got others

CMM MK9T 9MM 16.1 BLK 32 Hand Down...

Until recently, I've always gone with the standard AR platform, which typically supports .223/.556 ammunition. However, I recently purchased the necessary components for my first 9mm AR build from Palmetto State Armory. If you haven't purchased from PSA, I highly recommend giving them a shot. No pun intended! Haha. BUDS also sells PSA firearms and accessories and surprisingly, this isn't at much of a premium at all. Whichever route you go, I'd encourage you to go with PSA. Quality, customer service, aesthetics, VERY competitive price, and well groomed build kits are just a few reasons why I prefer this mfg.
As for performance, I've noticed a higher level of accuracy with the 9mm platform. This may be the result of a smaller caliber but overall the entire process is much smoother than firing .556 or god forbid, .762. Your should will certainly thank you! 9mm is going to be slightly more expensive than the aforementioned ammo but keep in mind, 9mm can be used in a wide array of firearms. I found peace in dual usability by using the ammo in my AR & Beretta 92FS. Knowing the ammo has flexibility adds some comfort when buying ammo in bulk. I.e. Wifey wasn't too happy with me purchasing 1000 rds of Wolf 9mm but I considered this to be an excellent investment! Haha.
All that to say, much of the 9mm platform is very similar to any AR you may have experienced in the past. If I had my druthers, I'd stick with the larger caliber M4/AR15 ammunition. Godspeed Sir! -Mike

Randy - there are just so many different models available for many different manufacturers. I'd suggest just searching Buds web site, and reading the reviews for the ones they sell. The "best choice" depends on so many different things, and is going to mean different things to different people, depending on what you might want to use the rifle for. It's sort of like asking "Looking at getting a pickup truck. What's the best choice?" Only you can decide what is best for you. Buds should be able to fix you up though. budsgunshop.com/catalog/advanced_search_result.php?keywords=AR+9mm