So you'd recommend having quite a bit of experience with CISCO kit before looking in to studying for the exam? All our routers are CISCO but they're all preconfigured by our Data Centre.
Packet Tracer or GNS - will do the job, its alright having experience with equipment but how much do you have, troubleshooting is just as important as configuring, + ive always used CLI, ive used SDM once and tbh i couldnt use it if you asked me now. You really have to graft through the curriculum too, i also used cybex CCNA book to revise from. CBT nuggets ICND vids for subnetting. You need to be able to subnet really well too, i had a lot of questions on this, some simple and some complicated.
Like DMS said though, sims are hard. The one on VTP gave me a run for my money, had to answer 5 questions, some were simple, like...what port did switch 3 associate with mac add.... was simple enough to answer, show mac add table and theres the answer. But there were a lot harder ones in that sim which required a bit of thinking and a few different commands to be issued.
I also had one on ACL's which involved creating an extended acl and applying it to an interface to block http traffic from certain hosts. i find acl's pretty simple though and im pretty good with them at ccna level.
My other sim was Eigrp which was remove and re apply, no router eigrp 22, router eigrp 212, network ... network ... no auto-summary etc etc. had a bit of trouble with that one getting it to form a relationship with a neighbour after applying network statements on both routers, spent about 15 mins getting it to work.
Im quite glad ive got it, as basic as it now seems. Proves i can do it.