I did this for a friend last week and he has the same plan. I used epc.tmobile.com.
We were told by Tmo themselves that this may take a while to get the internet. Sure enough after 30 hours it popped in.
So my suggestion would be leave the settings with epc and see what happens. You can also call Tmo and they will help you, they have an smart phone tech support and if your paying take advantage of it.
Good luck.
Thanks for all the help I put my sim card back in original tmobile phone connected to Internet then put sim in iPhone internet works now but data roaming charges must be on is that normal?
Not sure the fastest APN (I think they're all the same) but if your paying for the smartphone plan and u have problems using the internet or if its slow you can call T-Mobile and tell them and they will let you know what might be going on.
But this site is great for those answers too.
I have the sidekick plan (hiptop APN) and rarely have any issues with speed so you should be fine using epc APN.
To be honest, at home I get tops like 32kb/s with my 2wire router. So if the unlimited data plan or the sidekick plan or even the G1 plan get around 100kb/s, I'll be more than happy.