To provide a different perspective to the question, there is no best wallet to "keep" bounty tokens in, you don't keep tokens in a wallet.
Your ERC20 tokens are stored on the blockchain, it's a case of which is the best UI to access these tokens, as opposed to keep them.
To simplify: your tokens are kept on the Ethereum blockchain, not in a wallet. Wallets are used to access or transfer tokens, nothing else.
To view your tokens, use EtherScan or similar. To transfer/access tokens then you'd need MEW with MetaMask or a hardware wallet.
You can also use Mist running an Ethereum full node, but the software is still in beta testing mode so isn't very reliable.
All the best!