It's possible to install Horde/Roundcube/etc onto your webspace, too - no need to rely on your host for it. All you need is a host which lets you do so, which I'd suppose the majority do
Also - there are plenty of sites offering "comparisons" of hosts, but the problem is they're all funded by advertising...from the hosts they're "reviewing"....and as such not worth the (virtual) paper they're written on, unfortunately.