Electrum is without a doubt the best, its enough for any of you that think different to check the alternative clients both section of Multibit and Electrum you will see there that a lot more problems happen with Multibit than with Electrum. With this I don't want to say Multibit HD is bad , not at all but just want to underline less problems from Electrum as for the security both have seeds and allow a top notch password very difficult to be hacked by brute force. In security they are both very safe, but less problems happen with Electrum and Multibit HD is more prone to problems from what I have seen in the Multibit section.