I spent years on Android smart phones and all experienced the exact same behaviors, slow down over time, memory leaks, buggy native text messaging and then ultimately a bricked phone unable to place calls. I switched to iPhone 6 Plus over a year ago and I can tell you I’ll never go back to POS Android devices
I’m really happy with Android 4.2 and up and recent hardware - pretty much any phone or tablet with 1 GB RAM or more. 512 MB definitely was not adequate. We like our Chromebooks also, for that matter.