I think Jeremy has succinctly summarised things rather well. The FSI is more complex with more sensors and internal gubbins that complicate diagnosis (and incur costs) if things go wrong. It is perhaps more delicately balanced too and very sensitive relying on premium fuel and injector cleaning to get the best out of the engine. It is more punchier than the 1.4 overall and nudges the fuel economy stakes. If it is to be a daily driver then the 1.4 is the more reliable of the two as a rule of thumb. Again, if financial efficiency is a major consideration, the sensible gamble would also point to the 1.4. The FSI is a joy when running smoothly mind and I don't regret the choice; albeit I am fortunate enough that my car isn't my main daily commuter. As is always the case, service history, condition and enthusiast owned should be at the top of the list whichever option you take.