Sphere 1.0 is finally out? Is it every bit as wretched as the 99 series? Everytime I hear you and Rose say "well, Sphere is good if you use the 55i improved versions, but stay away from anything newer" it reminds me of the biggest reason I left Sphere behind; it has no future.
I would recommend RunUO for sure to anyone new. If you don't know C# then learn it. Start small with your custom scripting. Download scripts that other people have made, try them out, see what they do, tinker with them to make them do what you want, learn how to write your own from scratch. I can see the argument of staying with Sphere because you already have a lot of time invested in systems that work for you, but I can't see advising it for a noob. Yes, it is easy. Until you want to do advanced things with it, and then you need to invest time learning how to make scripts that do what you want. RunUO is also easy right out of the box. Yes, you also need to learn the scripting language, but because it is a real programming language there are also already utilitys out there to help. Orbsydia's tools that are in development are built from the groundup with RunUO in mind as well. Anyway that's my 2? worth.
You should of course look at them all and decide for yourself. Besides RunUO and Sphere, there are also POL and UOX (and since UOX is opensource there are many flavors of it, kinda like Linux).
http://www.polserver.com/
I don't know for the life of me where UOX's homepage is. I see uox3.com is still owned by Ryan; hence it goes to RunUO (which is not a UOX spinnoff).