I use all different clients for all different reasons.
Razor is my main one, I use it because I like the simplicity of it. I can have it automatically take a screenshot half a second after I use my stealing macro, so I always get a screenshot of my steals. I run this on my main character pretty much all of the time.
I use UO Steam for PvM because it has a great autoloot feature that helps me pick up all the little gems and bits of gold that just aren't normally worth the trouble to loot. I usually use it on non-thief and non-crafter characters.
I like Razor Enhanced when I feel like programming something. I don't often use it because I find it to be more than what I need but if I ever were to do something complicated, this would be my go to option. I mostly program in C# and the IronPython scripts used in RE can import some .NET libraries that I am used to using which makes it more convenient for me than the JavaScript options that Orion has.
When I play free shards, I like Classic UO. I understand that they may have the life bars updating for official servers now which is nice. I wouldn't use it on my main character though because if I posted any screenshots from it on Stratics, the 3rd party program police would crawl out of the woodwork to whine about it. I don't really care what they think, but I really hate having my posts deleted.
Between all of those programs, I can get anything done that I want so I have no real use for Sallos, Orion, Stealth, EasyUO, and whatever else there is out there.