Anybody switch from T-Mobile to ATT, or vice versa?

I'm not thrilled with my T-Mobile coverage, thinking of switching to ATT. Wondering if I'd realize a noticeable improvement? Has anyone tried both?

Or does upgrading one's phone itself help?

Edited to add: I'm gonna discount the new phone idea upfront on the ground that other family members, with more current phones, fare similarly.

When I went from T-Mobile to AT&T I definitely noticed fewer dropped calls but I also upgraded my phone.