Matt,
I have a Unicender but not a RopeWrench. I am getting a ropewrench to try (I havent yet so there is some ignorance in my comments) as well as a spiderjack and am going to attempt a 'buying guide' video featuring the pros and cons of all of them.
Price: The HH and RW are about the same price all said and done when you consider the stiff tether and a biner for the RW. The Uni is considerably more expensive.
Durability: The HH is extremely well built and will likely last forever. The friction bearing aluminum component is so wide and broad that wear and tear for me, in daily use is unnoticeable and the tool steel portions show no wear at all. The RW1 and 2 both seem like quality products and the RW has seemingly all replaceable & affordable wear parts. The RW2 incorporates a moving part, the pulley, which will eventually wear out or get gritty or something, however I imagine the lifecycle is quite long. The Unicender will most definitely wear out and require a rebuild within 1-2 years of use, maybe less..
Versatility: I have spoken a lot about the HH's versatilty, I could elaborate but I am sure you get the idea. The RW I dont know much about its DRT performance but I have never heard of someone using it DRT except for arial rescue, however inherent in a RW setup is a DRt setup so removing the wrench leaves you in DRT mode. The Unicender is really versatile, it easily switches between SRT and DRT much like the HH.
Performance: The RW has documented high end performance and is notoriously customizable. It is longer than both the Uni or HH. All the video and review I have digested on the RW show that it tends smoothly and grabs reliably when used properly. The setup is quick and the RW and tether stow well. The HitchHiker for me is very intuitive of my normal DRT hitch setup, I place a lot of value on its compact setup and familiar feel. The hitch configuration required fine tuning for me in the beginning but I have everything dialed into a consistent reliable setup now. The Unicender for me was a little hard to get used to. My unit was used when I received and I have tried it on fat and skinny lines. I was never able to get a smooth feeling on it and always switched back to DRT. The Uni is great for me for setting crane picks and climbing small trees DRT. It will self tail better than any of the other devices in question. As far as weight the HH weighs the most and the RW weighs the least.
Overall I like the HH and to me it is a clear choice over the Unicender. I am really excited to try a RW in the coming weeks so I can learn more about that, I am going to be using a RW1 so if anyone has a RW2 that they would loan me I would really appreciate that.
In truth, for me personally, I dont think the performance of the HH could be so greatly improved by the RW (or anything) that I would give up the feel, setup, and size of the HH.
I think Adam has all 3 devices you mentioned, you should give them all a try. Let us know what you decide!