Given an equal starting point, I would say go with EFI, without a doubt. I love my triples to death, but when I rebuild the engine, the Mikunis are going to get cleaned up and put into storage. They can be hard to tune, VERY temperature sensitive (especially with more agressive cams. You don't aim for a idle RPM so much as an idle RPM *range*.
Also, you aren't going to get a goot triple setup for 600 bucks unfortunatly. Last set of triple mikunis I saw for sale was ~1500. You're also going to be looking at spending around that much for a good ITB EFI setup (though you'd still have to get a fuel tank, new fuel lines, etc, etc, etc).
Also, while you might like the shorter stroke of the L24, with modern con rod bolts and the additional power per cylinder, the L28 will be just as rev happy.