2ZZ-GE or 2AR-FE
Personally my goal when i developed the 2AR-FE swap kit was very much about daily driveability and reliability. Power is a consideration of course but it isn't the #1 consideration. I also wanted to make something with way better quality parts than the k-swap parts that people were breaking repeatedly but hadn't seen a design update in several years despite the repeated issues.
At the same time i took all the feedback from the 2gr-fe stuff over the better part of a decade and wanted to address all the friction points, especially things like wiring difficulties.
I think i pretty much nailed all the design criteria with my parts, including the body controller that makes everything work as it should and makes it so the factory wiring does not need to be touched. The big thing is this swap kit can be installed by someone that has never done an engine swap and they can be done in only a single weekend of downtime. Michael did his swap in two weekends.
I've been racing the 2AR-FE since 2009 (less than a year after it has been released by Toyota) and it's been super reliable at elevated RPM and power levels. Don't get me wrong, i wish i managed to get a bit more power from it right out of the box but 205rwhp (roughly 235hp) is pretty good for a Spyder. In a car this light i have no problem pulling away from V8's and V10's on the track.
Cost wise, it's going to be impossible to beat a simple 2zz swap, that will always remain the cheapest swap. I know i've caused some shake-up in the k-swap parts so i'm not 100% sure if the k-swap or the 2ar-fe swap is cheaper at the moment. Last i looked it was a touch cheaper to do the 2AR-FE vs a k-swap even if you use the cheapest K20 engine (170whp or so) so you get a bit more power for a bit less money. And of course if you build that magical 240whp K24 build you're at about $4-5k more than the 2ar-fe swap would cost. So for that extra money the 2AR-FE could get some work also and gain power.
Of course the issue is the 2AR-FE's power gain routes are only documented for turbo builds and to get to 350-400whp. The motor has been proven to 800whp and 1000whp levels but those builds are not well documented at all.
And finally, don't forget about the transmission. This swap comes with a wonderful 6 speed transmission that is just fantastic to drive on the street as well as being super durable on the race track. It's a bit of extra cost to swallow both upgrade costs at the same time but in the end you get a way more reliable car.
I will be documenting a 2gr-fe swap for the Spyder using these parts but that's more of a marketing thing. My race car will be getting upgrades to the 2AR-FE instead because i'd rather be racing that motor.