Never one to miss an opportunity to promote my own sim, here's a link to it : http://www.h-net.co.uk/tsim/ - it takes up less space than Crocs. which is admittedly highly impressive but a bit complicated for a simpleton like me
I've used the PFG sim, and it can be tempermental sometimes! I believe it is hosted on a separate server (not part of their main trading server farm) which is unattended - so if you phone and tell them the sim server is down they fix it; if you don't, you have to rely on someone else doing it. But apart from that, they are pretty good.