Doopy's seems to be one of the easiest to build but you can also do a pipe scratch build with the addition of some doopy pieces or even sterling replica pieces. If you are only aiming for EIB than a hasbro mod would be fine, I want to go for Centurion so my hasbro is not good enough so my new project is a pipe build with doopy pieces.
You can also spend some time gettting ready for your brown box to arrive by sourcing things that you will need for you build. I have most of my snaps ready, just made a thermal detenator, also made, belt, holster, neck seal, there is quite a lot to do. I was lucky enough to purchase my helmet seperately to give me something to start on, may be worth a try asking your armor maker if you can do the same.