From initial reports, the Portapro and Portapro 2 are identical sounding, or nearly so. The KSC-35 is a more neutral, somewhat less bassy version of the Portapro, using the same drivers. Personally, I'd go for the KSC-35 unless you really like a large amount of bass. Any of these headphones are tremendous values. I personally prefer the KSC-35 to the Grado SR-225. (It's not that the KSC-35s do more things better; they don't. But they also don't have some of the odd tonal flaws that the SR-225 does. I know I'm in the minority here, but the point is that the KSC-35 are really quite good especially for the price.)
There are two negatives that I've heard about those headphones. Supposedly, when turned up to a comfortable listening volume, the whole bus ur riding on hears exactly what you hear. I don't exactly want that kind of attention. Also the Portapro/2 are supposedly to be very prone to breaking.
All these are open phones so yes they leak, especially at high volumes. There are worst phones in this department (I use my PP2 when the Alessandro leaks too much), but if you want to avoid that completely, you're going to have to go closed. Maybe the Beyerdynamic DT 231, etc..
Otherwise I preferred the sound of the KSC35 slightly, but couldn't handle the feel and tension of the clips, so went PP2.