2ZZ is a badass motor. With the 2000 Celica GT-S ECU you get lift at 6,000 RPM and redline at 8,250 RPM. It screams. Lift kicking in is a nice feeling. It's a really enjoyable engine that makes good power.
It is a bad ass motor. But it has its flaws.
MMC lined cylinders. Can't be machined if the get warped. Sleeves need to be installed then bored out for more ponies.
Front oil pump, design flawed as it gets destroyed due to low oil if the previous owner kept oil levels low or just trashed. One of the biggest causes of death to these motors were miss shifts.
Oil pan doesn't have a baffle. Can always modify a 1zz pan which has a baffle. Go figure.
Though the 4age is older, it was designed to take more power by design. It's not as high revving as the 2zz. The only issues that I see is finding a complete harness and ECU. If you check your local Craigslist and will find a 20v with trans, harness, engine and ECU. Might get a deal there. It may cost more in the long run to get more power gains on a 4age, but it's a cast block and internally stronger.
The 2zz is cheaper due to newer tech. You want this set up, best to check the local salvage yards.
Best engine to source is 00-01 Celica gts. It's because this is the highest hp engine out of the 2zz family of engines.
If that can't be located, then 03-04 matrix xrs or Pontiac vibe gt. These were rated closer to 180hp and didn't have the air injection set up and the lift point was lower.
Then finally, 05-06 Corolla xrs. This was the lowest hp offering for the NA market. It's 160hp as the Corolla is your everyday commute model. Not sure why it was detuned for the Corolla.
You could unlock the potential by using a Celica GTS ECU with the 2zz out of any above. Just make sure you use the harness also. As mentioned before, the celicas did not have the air injection pump at the end of production.