Both powersources are top of that class. Your going to have to look at little things that may set them apart, such as auxillary power outlets and the cost optional of push-pull guns for aluminum and overall costs.
You won't be disappointed with either choice.
Another thing to consider is what you will be using the welder mostly for? The 250 is the max amps, which will give you alot of welding power for welding heavy thicknesses of steel together easier. Then there are welders for fabrication and there are welders for in shop 220, raceway 110 all in one. There are welders for autobody work that only go up to 0.35 liners wires that are just as powerful as the Millers etc. Powerful meaning uses 200 or more amps pulling less out of the wall. Every company has innovations pick the one that has the features you want. I bought an HTP. Check there website out to compare. Clark makes good welding machines also that i know of for body work. Hope this helps