I use both, I have a mag 256 and a quad core android with STb Emu. In my opinion the mag is very slightly quicker at loading up but thats about it. I have found them both very reliable, and as to picture quality might be my eyes, but they seem the same. I have had the mag about 9 months and it has never crashed, the android stb emu has crashed a couple of times but thats probably over a similar time scale so nothing to speak of. The big difference for me is the versatility of the android as I have a cheap netflix (fleabay) account, terrarium and showbox + when using the last two of these I have a vpn. I don't need a vpn with either of my subs but thats at the moment, things may change. Its a lot cheaper and easier to have a vpn on individual devices if and when required than investing in a router fast enough to have a vpn installed as you would need for the mag.
In short given my personal experience I would not buy another mag, I would want something with more versatility as you get with the latest android devices. Its your own preference, if its purely for iptv the mag is fine.