I feel inclined to contradict the general concensus here and say that the front mech is more important than the rear. In my experience a flakey or badly adjusted rear mech will at worst produce some chain noise and the odd chain skip on the rear sprockets, bringing you up or down a gear....that's not a ride threatening situation. However, if your front mech plays up it's likely to manifest into a situation where you're stuck in the large or small front chainring due to a sticky spring, or worse, your chain is thrown off completely.

Also, I disagree that all front mechs are the same. I rode last winter using a Sora front mech that would perform perfectly AS LONG as the temp stayed at reasonable levels. As soon as it turned frosty on cold Scottish mornings the mech would just sieze up and I'd be stuck in whatever ring I'd left my bike in the previous day. No amount of lubing would help and I'd have to physically kick the mech to make it budge.

When I swapped it over to a 105 front mech these problems vanished. Overall the 105 mech just seemed more reliable that the Sora and performed consistently in all weather conditions.