The 1000 and 2200 have the same 5 gears in the tranny, only difference is the 1000 is good to 19500 GVWR and 26K GCWR , the 2200 is good to 26K GVWR and GCWR.
The 210 is rev limited to about 2600-2800 RPM vs the 300 being able to get into the mid 3000 range. SO yes, the 210 will give you better mileage, BUT what are you using hte truck for? Pulling a trailer, then the 300 from the get go would be the better choice, if using it as a Truck mover, ie the truck only, then the 210 could be a better way to go.
If you need more GCWR than what those Allison trannies offer, you may want to look at the 6500 or 7500 with the 7.8 dmax I6 or the 7.2L cat motors, THen you can get a 2400 allison (33GV/GVWR rating) in some instances with a lower first gear, or the 6 spd version of it in the 3000 series with a 40-80K GCWR rating.
THere is not a right or wrong way, other than how you will use the truck, either could be the wrong rig, one could be right, or both could be right. How you use it, what you are doing are the big factors in choosing an MDT.
MartyB
05 DW3500 D/A crewcab
2000 C2500 reg cab 350/auto
mem# 2825