MyHorseClub is OK! But I found one that's better...
RidingClub Championship!!! It's got better graphics than MHC, but the only downside is you have to pay to play it. It costs only $6 a month in the US. That's not too bad, and it's a whole lot more fun I think.
MHC just has too many problems with servers and things not working right. It's fun, but can really be frustrating!