The 1.6 is much better to drive. The 1.4 tends to be more difficult to get moving at junctions without juddering or over-revving. Not a huge issue but noticeable nonetheless. The FSI is also considerably quicker when you want to give it the beans, provided you move through the gears (110 bhp vs 75). Due to the lean burn, the FSI will not accelerate well if the engine rpm is low (in a higher gear) and it can almost feel like turbo lag once the revs rise and you get more power. You don't get this to nearly the same extent in the 1.4. The 1.4 is about 80 kg lighter as the engine block is aluminium, whereas the FSI is cast iron, which makes it a bit more front heavy but I haven't really noticed this driving normally. The higher rev limiter (over 6k) means that you're less likely to need to change up when overtaking, which feels better.
Motorway driving isn't too different, as the gear ratios are very similar, so rpm will be about the same for each car at a certain speed.
With regards to fuel and fuel economy, the 1.4 isn't too bothered by what petrol you use (though super still seems a bit better) whereas the FSI wants Tesco momentum or Shell V-power. Using regular unleaded gives worse performance and 10% worse fuel economy, so isn't worth it at all, and I've even found that 97 RON super is worse than 99 stuff. If you drive the FSI carefully it gets better fuel economy than the 1.4, but equally I find that being a bit more careless actually makes it worse than for the 1.4. Still, the difference isn't huge.
I haven't had a reliability issue yet with the FSI, but I've only had it for a couple of months so we'll see...
