I've been using Pinta, but I find it slow to open (Paint is also slow). Is paint.net quick to open? I'm talking 1-3 seconds; Pinta & Paint take 6-10 seconds. Granted, this is on a work machine with a bunch of AV and other things slowing it down.

Paint has gotten some surprisingly decent updates in the past few years, same with notepad (tab support etc.), so of course Microsoft had to sabotage themselves before people realized.