nokia c6-01 is a good phone.. the phone will be eligible for upgrade to the next version of the symbian operating system, Symbian Anna.. battery life is good in Nokia phones which can be an added advantage over galaxy ace..
as i mentioned earlier, galaxy ace is an android-based smartphone.. so u may get all the features at the cost of a poorer battery life..
so if battery is not a problem for you, i will suggest you to go for galaxy ace!!