I test drove a GTi, and I mean no offense by this, but I hated it. The suspension was stiff, it felt slow, it felt cheap, it was sort of boring, not much excitement.
The 128i is just a 135i with less power. It's often praised in it's own right for being the most "true" BMW because it's small, relatively light, RWD, and normally aspirated. The interior is nice, the ride is good, the styling is good, the engine is good, just don't get a 128 with a steptronic. The auto in the 128 is a GM unit and not the same as the previous 135 steptronics. The 6MT however, is good.
Depending on what options you want, the 128i may not be much cheaper than a 135. In my opinion, the only way to get a 128i is to get one without all the bells and whistles. 128i, sport package (not M sport), 6MT, that's it. Once you start adding, the gap between 128 and 135 becomes so small there isn't much reason NOT to get the 135.
2007 SLK55 AMG - Black on Gray/Black - AMG 030 Performance Package
2011 135i - Traded
///M-Sport - Dual Clutch - Harman Kardon - Bluetooth - iPod - Shadowline Kidney Grill - 225/255 Star Specs - Hotchkis Front Sway