QT Core is good only for folks who can keep it on and connected to the internet all the time...you break it for one day and it takes 15 minutes to sync
Multibit is a good choice
some people dont turn their computers off anyway for other reasons and most western houses have wifi thesedays
i have multibit as well but i like to run a full node anyway to strengthen the network
i think its only a matter of time before the current blockchain is pruned or compressed into something more managable etc because new users will have no need to store every transaction of the last 7 years