If you want somewhere to save large amounts of bitcoins I recommend you keep the bulk of your bitcoins on the Satoshi client. It is the most mature.
The light clients all have strengths and weaknesses:
(disclaimer: I develop MultiBit)
Electrum - if you are interested in deterministic wallets have a look at this one.
Armory - probably the most advanced client but is quite resource intensive at the moment. Multi-wallet.
MultiBit - straightforward, lots of languages, multiple wallet. Wallets not encrypted yet.
Blockchain.info is very nice for an online wallet. They develop new features at an enviable rate.
Instawallet works well when you just want a simple one address wallet - I use it on my iPhone.
There is a great choice and none of them cost a single cent.