On the one hand I like GOG because it has no DRM and has better prices (in my country) than Steam and I have the feeling that on the one hand it follows more the open source philosophy than Steam itself, but Steam has helped enormously to play Windows games on Linux, so I haven't really made up my mind.
On the one hand I want to buy on Steam for the convenience, but on the other hand I prefer GOG because (in my country) is cheaper. Which platform do you prefer and why?
To give an example, The Binding of Isaac: Rebirth is currently $15 on Steam with regional pricing, but on GOG it's worth just $6.
I go clientless with GOG, too - but their download speed was atrocious every time I tried. Steam nails that, unfortunately...
Infuriatingly, steams constant updates and massive start up delays (we have multiple users with different accounts) straight up sucks - we'd be better off suffering the one-off download delays, really.
Cloud saves are amazing, but I try and launch stuff not through steam as its just a slow, bloated old mess I can't stand dealing with (I'm also quite OK with migrating data around computers and keeping it stored safely)