sorry to be the bearer of "good news" here but you can download a Protools demo:
http://www.m-audio.com/products/en_us/ProToolsMPowered71-main.html#download
You need to have an m-audio interface (the site shows you which ones are compatible). I have the delta 44.
At any rate, I've been challenged with this same scenario. I use FL studio, but have looked into all three of those DAWs you mentioned for recording vocals and mixing down my tracks. I have actually used Sonar 4 for a while now and I'd say it's an okay program for what I mainly do. I did download the both the ProTools and Adobe demos. I would say out of the three, I am leaning towards Audition. My 30 day trial of Audition is about to expire and I'm dreading having to slap down the $350 to purchase the sh*t, but I definitely give it the nod. It seems like you can do more with Sonar 6 in terms of midi and some other things, but the interface is just not as intuitive as Audition. Also, Sonar 6 kinda looks "cartoonish" to me as well. It seems like they have tried to make the user interface more user friendly, but I'm not really feeling it.
I would say that if you are comfortable with Audition, and you mainly work with Audio files (e.g., .wav's), I would stick with that. If you are looking to expand into more midi instrumentation and video and all of the other features of Sonar, by all means explore that option. I've found that the best creativity comes when you don't have to keep trying to figure out how to use the stuff you got. It just works for you and you can concentrate on the music - y.., y.., yeah