I've driven the 100bhp 1.6, the 1.8 and own the 115 1.6.
The 100bhp 1.6 engine is woeful in the MK2.
The 115bhp 1.6 VCT engine is fine, however. Ok, it isn't going to blow your mind, but for what a Focus is generally used for, it is more than ample. No issues with four passengers, either.
That said, the vct takes a fair old economy hit over the not-vct. It isn't far off the 1.8 for its economy figures, which makes the 1.8 seem like a slightly better prospect as that little extra torque certainly helps.