Start with the EJ22T if its a bare bones build including rods and pistons. Crawford says they have a new no-slap forged piston, so thats the way I'd go. I'd use a phase 1 EJ25 crank while I was at it and end up with 2.4l I think the best thing about the EJ22T is the oil squirters for the pistons. It helps keep the temp of the pistons down and more uniform, reducing the chance for knock.
The USDM 2.5 is the simple way out. You know its built right by the factory and its a brand new block. Its also cheaper than a full EJ22T build. Crawford also makes pistons for this motor for use with WRX heads. They bring the compression ratio down to a reasonable 8.0:1