The obvious thing here, I hope, is that you will want to go RTK for control. This brings you first to three options. Trimble FmX or a TMX with WM-Drain, AMW(AgPS), or AgLeaders Intellislope. Once you pick that you'll know what you need to do. The Trimble outfit is all Trimble hardware and software. I don't know of anyone or many that are using different hardware components if they are running Trimble's WM-Drain. The other two can use your Deere antennae more easily. I'm sure your biggest factor will be price. I would suggest you try to find people that have each of these systems and ask them what they like and hate about them. You probably have a dozen neighbors with Intellislope, a few with WM-Drain and maybe fine a couple with AMW. Check each of them out. Keep in mind that you want to have a base station as vertical accuracy is very sensitive. I know too many that use their Deere RTK and don't have a base station. The nearest one for them is definitely over the 2mile distance that we consider the maximum distance you'd ever want to be from your base. You can find many different forums already on here debating the three systems and RTK in general. You will also want to keep in mind the design software for your computer that is made to operate best with each.

http://talk.newagtalk.com/forums/thread-view.asp?tid=603156&posts=6#M5016642

http://talk.newagtalk.com/forums/thread-view.asp?tid=613133&posts=7#M5122236

http://talk.newagtalk.com/forums/thread-view.asp?tid=635137&posts=3#M5322771