If you are set on getting a modchip, take a few things into consideration.
First, is the install - probably the biggest factor in your decision. Are you going to be soldering or go solderless. If you have the tools, skills, and guts to do it, I would recommend soldering in a modchip. I am not the biggest fan of solderless modchips. Sometimes you have to open up the box again to readjust them.
Second thing you want to think about is if you want an OS or not. Newer chips will have an integrated operating system with useful functions like the ability to load different BIOSes, lock your hard drive, format hard drives, change settings, connect via FTP, etc.. None of these OS features are exclusive though. You can do all of this with something like a SlaYer's bootdisc if you wanted to. You're just paying for the convenience basically.
I personally prefer the DuoX 2 chips because they are very cheap, can be installed in any version Xbox. They don't come with an OS, but that is not something I need.
For the most part, all chips will do the same thing in the end, get a hacked BIOS on your Xbox allowing you to play backups of Xbox games, run homebrew programs, emulators, etc.