Gmail

Fuck it, I'll give it a proper review, because why not? It's not even the worst provider out there, if you can believe it. It does support mail clients, for one - so it automatically has an advantage over many of the ones advertising privacy and user respect that are webmail-only. My VPN was not blocked, though it did ask for my real name (which you can fake) as well as requiring phone confirmation - which I ended up choking on.

Unfortunately - as if it wasn't obvious - mail client support is the only positive Gmail has. Well, it's also free - but you pay with giving up an amount of data which other providers can only dream of matching. For example:

unique identifiers, browser type and settings, device type and settings, operating system, mobile network information including operator name and phone number and application version number. We also collect information about the interaction of your apps, browsers and devices with our services, including IP address, crash reports, system activity, and the date, time and referrer URL of your request.
We use various technologies to collect and store information, including cookies, pixel tags, local storage, such as browser web storage or application data caches, databases and server logs.

There is much more. It's not an exaggeration to state that every step you take, every move you make while using Google is stored and analyzed (and the duration is not stated, as far as I can see - so assume it's forever). What makes it worse is that you can't sign up just for Gmail, but need a Google account for every one of their services. So, if you're logged in (because you're using their webmail, for example), then they can also track you all over YouTube, etc. and mix up all the information to make a profile. Google is also a PRISM member, so your stuff is likely ending up grabbed by law enforcement (they've shared location data with them before). And, using Google's services means you enable all their unethical practices (such as shoving ReCaptcha into our faces, heavy censorship on their search engine, widespread tracking and ads, their monopoly on browsers, etc). Other providers - even those of the spying sort - pretty much limit themselves to mail; they don't have the worldwide influence on so many things as Google does. So, you should specifically avoid Gmail just to inhibit their quest for world domination (did you know they can even lock you out of your house?) - even if they're not the worst provider out there.