So, basically people really love using XP and 2003? But VX Ace is the newest and has the largest number of functions?
Nope, all wrong. But we replied more or less at the same time, so I guess you haven't read my other reply
In release order, from oldest to newest, it goes: 2000, 2003, XP, Ace, VX Ace, MV.
2000 and 2003 are rather old and outdated, I wouldn't recommend them. They're also less flexible since they do not have programming. Back in the days, I used them because it was what was available, XP did not exist yet.
Some people prefer using XP because of some functions that have been removed or modified in later makers. But it's more limited in other regards (I couldn't really tell, I never used it).
The newest (and possibly the most powerful?) is MV.
Although VX Ace is still very powerful and there's a lot of assets for it.
Aside from the early development of these products, said that there will be more in its functionality over time right? Then this means MV can still have more... uhhhhh... like more tiles, effects, sounds, etc.?
Don't get me wrong, MV is fully functional. They are still working on adding some stuff in (I couldn't tell you exactly what, I suppose there's a changelog or roadmap available somewhere?), but you are not going to have a buggy beta software if you buy it.
As far as assets go, what you have to understand is that a lot is made and shared by the community. VX Ace and previous softwares have been around for years, so a lot has been created. Also, they used the same resolution for graphical assets, so stuff created for XP could be used in VX Ace. MV changed the resolution, so everything as to be rebuilt from the ground up. It's less noticeable with scripts, maybe since those are version exclusive, but MV is still the newer addition and less material has been made for it yet. But people are working on it, there's more with every passing week. And by assets, I mostly mean tiles, sprites and scripts. Sound and music too, of course, but I think those are more universal and could be used regardless of the maker's version. Required file types might vary, I don't know, but that's manageable.
So personally, I'd recommend either VX Ace or MV, but I guess XP is also a viable option. I'd say get the demos for these three, see what they look like, test them out a bit.
Also worth noting, game projects cannot really be transferred between makers. If you start something on XP, don't expect to be able to convert it to VX Ace or MV. But don't let that stop you from really trying all three makers, as a beginner you'll likely start over a lot as you discover new functionalities and become better anyway.