If you keep the height and width down you won't get those nasty scroll bars.
I think you can go as high as 250 pixels before they kick in. Maybe it's only 225. If you keep the height to 200 or under you have room to add some temporary text above or below your picture. Like for example "I'll be on vacation. back on August 4th."
Width seems to start scroll bars beyond 500 pixels.
You don't need the best editing program or the supposed "Best-choice". Depends on the way you learn. I figure its a little different trying to figure out GIMP than learning photoshop. When I was younger I learned photoshop quite easily. So go for your own style I suppose.