Mail Pilot vs eM Client

There are options to display URLs you get in emails, or to disable pictures by default if you are afraid of getting malicious data from suspicious emails.

Mail Pilot turns emails into tasks. It has a built-in system of setting reminders and collecting emails into groups as to-dos.

Such as sorting through categories, etc.

It is free for 2 accounts and as long as you don't use it commercially. Paid version comes with support and can handle more than 2 accounts.

They've been developing and improving it consistently for years.

eM Client seamlessly integrated the Quick Text extension that was available on Thunderbird. This makes it easy to quickly auto-insert dynamic text, based on many variables, saving time and the need to tediously repeat manual text replies.

eM Client includes integrated chat, so you don't need another application for chatting with your friends. All common chat services supported (Google chat, Jabber and others).

eM Client sends straight .pdf files for fax messages flawlessly.

It saves space, unlike Thunderbird.

But only because it has no alternative.

It provides (almost) complete Gmail functionality (calendar, tasks, chat, contacts), while offering advantages of an application: offline use, more e-mail providers in one place, very good design, support, etc.