the biggest difference is the 1J is 2500cc's and the 2J is 3000cc's, some say the 1J head flows a little bit better but nothing porting on the 2J head couldn't do. The 1J is bit more rev happy due to having a shorter stroke but it will have less low end torque and wont spool a big turbo as quick as a 2J.
I would get a 1J though because they are so much cheaper.
thx i probably will go 1jz because ive called around and nobody seems to have a 2jz
i just got off the phone with jdm of miami and they gave me a price of 5000$ for a 1jz 6speed holy shyt just for the package not installed
i got jz parts