advantages and disadvantages
hmmm...it would depend on how much power you're looking for and what kind of power. The ej25 is capable of more low end torque than the ej20 but you'll probably lose your transmission faster this way.
Looks like the ej20 swaps are getting pretty popular too, plus it'll be smog legal (A big PLUS in cali).
When you're asking for big power, reliability is gonna be a problem either way with the ej25 or the ej20, and it'll probably come down to which engine behavior would you prefer (if you have the money to do either mod -- engine swap or ej25 turbo)