The most popular question for all of the Lumia users, old and new is, "Should I upgrade to W10M or keep using WP 8.1?"
Well, I have 2 Lumia phones with different OS's, a Lumia 930, running Windows Phone 8.1 Update (aka GDR1 or 8.10.14226.359), and a Lumia 650, running Windows 10 Mobile 1709 (aka Fall Creators Update or 10.0.15254.603)
These Lumias were released in 2 years of each other, while being in different categories (Flagship vs Midrange)
So, first up, the lock screen, there's a difference already, on the 650, we have a shortcut for the camera, but it's basically obvious, since the 650 doesn't have a camera key, and it doesn't have the sweet physical touch buttons the 930 has, so we have on-screen controls, it is pretty nice that it can dissapear when you're watching stuff, but sacrificing a bit of space just for buttons is kinda mid.
Ok, where was I? oh right, the lock screen.
When we access the action control, we see that W10M has a whole lot more shortcuts than WP 8.1 (16 vs 4) and you can delete individual notifications, which you couldn't do on WP 8.1.
Next up, the home screen, and you can see why everyone likes WP 8.1 more.
So on WP 8.1, we have the most perfect way of showing off Live Tiles, they really have the perfect amount of spacing, the best way of animating those tiles and the phone really feels alive.
Meanwhile, on W10M, it just feels like, just another phone, tiles animate less "alive" (aka it just swipes up, instead of actually flipping), the spacing makes it feel crowded, and the People Tile just doesn't have that lovely animation I really get stuck watching, it just feels "meh".
Now, the setting app, kudos to W10M for actually organizing the Settings app, but there were trying to do that on WP 8.1, too.
You may be asking "What do you mean by that?" Well, there was an Update 2, WP 8.1 GDR2.
GDR2 (aka 8.10.15137.148) added Settings organization by categories, compatibility with Bluetooth keyboards, pinning individual Configuration in the Home Screen, MKV support in the Xbox Video app and an improved anti-theft system. It came out of the box with the Lumia 540, 640/XL, 735 and 830, and you can still upgrade, if you want.
Now, let's enter an app, and we see some different things, one of which, really made one-handed stuff hard. The hamburger menu.
The hamburger menu just hides the extra stuff from the app, but and hear me out, I like the WP 8.1 a whole lot better, since sometimes we all use our phones one handed, and the Nav. Bar on 8.1 actually had consistency with all of the apps, it felt like the app was part of the OS. Then when W10M introduced that hamburger menu, the consistency was gone.
Finally some bits and pieces, Lumia Camera on 8.1 got replaced by the default camera in W10M, the app exiting and opening animations are meh in W10M and the only difference in the keyboard is a little nub in W10 tha tlets you move between text.
Now, should you choose 8.1 or 10M? This is a little bit hard, but Low to Midrange, stay in WP 8.1, and Flagships, you can upgrade to W10M, but I'll tell you, your phone could heat up more in W10M than in WP 8.1, but why?
Welp, do you remember Fluent Design? So, that's the cause of the phone being more slow than normal, even that 650 runs so slow because of it's Snapdragon 212 processor, which was downgraded to get that AMOLED/OLED screen and metal design to a 199$ price, even the 640, 630 and 625 has a Snapdragon 400 processor at a great price.
Also, there was an 850 that was about to get released, but of course, in Microsoft fashion, it got cancelled. Well, that has a Snapdragon 410.
Really wish Microsoft brought back making phones, but of course, we can't have that, we still have a Duopoly, just like in 2010, but atleast we have a community of people trying to make modern stuff work on Lumias, and I know it's gonna get better from here.
Wait what do you mean they made a Surface Duo are you joking????