For Mail/Calendar/Contacts/Tasks you should really consider Evolution. I've switched ~2 years ago, and it's amazing. Stable, sleek, and with tons of options.

It has a bad reputation because, back in the day, it was buggy and bloated. But I haven't hit a single bug over these years, and while it eats a significant amount of memory, it's on par with other options (and these days everyone has plenty of RAM).

I'd love to see more people giving it a second chance.