I switched from an iPhone 3G to Samsung Focus.
Later upgraded to Lumia 920, then 1020. Waited forever for a new flagship that never materialized (and still hasn't).
Downgraded my 1020 to Windows 10 Mobile, reverted. Sold the 1020, figuring the 950 (still rumored at that point) would be out soon and fix the Windows 10 Mobile bugs (which, we all know, it hasn't). Got a Lumia 635.
The 635 was awful, so as soon as the 640 hit, and was on sale for $69, I snagged it. HUGE improvement. Still not amazing, but it's a solid device. Downgraded it to Windows 10 Mobile, still awful. Reverted back to 8.1.
Every new release of 10, I downgrade to 10, then revert to 8.1, because 10 is SO. Horrible.
November 2015 arrived, the 950 arrived to terrible reviews, Windows 10 Mobile still sucked, so I'm done. Android now.
Of course, Android hasn't been great either. The UI blows, and you can clearly see the flaws that now exist in Windows 10 Mobile came directly from Android (way to copy, Microsoft. Pro tip: Copy the GOOD stuff, not the garbage). To boot, my LG Gflex 2, which has nearly identical hardware specs to the 950XL, took a dump after barely a month of usage, so I'm back on my 640 while I wait for the Android phone to come back from LG's repair center.
I wish I could get the 950XL with Windows Phone 8.1 instead. It's so, SO much better than 10 Mobile.