Mozilla Firefox would be my preference as it's very reliable and less prone to peculiar things happening or "attacks" as many viruses are aimed at exploiting Microsoft products such as Internet explorer. I don't use outlook or thunderbird for email, as at work we have Linux so I use good ol' pine for email and at home I can logon to my work, hotmail or OER email accounts. So I can't comment on which is better for email. The only negative is the odd site is designed for Internet Explorer use so keep IE on hand for those situations.