In my experience - the difference between published apps and citrix desktop is negligable. If users are having to use multiple apps via citrix at once, then the desktop seems a good way to go, but if its just the odd app (outlook for example) then published apps are fine.
Thin client model has pros and cons - you would need alot of network bandwidth for this as everything runs over the network. And it can work out rather expensive if you are thinking of taking the PCs out and replacing them with thin client terminals (this isn't strictly necessary though)
Personally I prefer citrix desktop as it looks just as it would on Terminal Services. Also theres Citrix Session Shadowing which is the equivalent to VNC etc so remote helpdesk operators can see what users are doing.
Don't know if any of this is useful for you
