I started with Waded 1.83 and Doomcad 5.1 both horrible horrible level editors, esp Waded which would delete linedefs (on Doortraks). For general use I find GrafX2 is maybe a little too in love with the idea of imitating Deluxe Paint interface though. Occasionally I'll mess around with GrafX2 (a sort of Deluxe Paint alike) mostly in cases where I want to work very strictly within a palette (one thing GIMP's not that great at, lots of functions throw a fit if you try to do them in paletted mode so you end up swapping back and forth between palette and truecolor a lot.). Once you figure a few things out there are a lot of really useful things you can do like realign a texture to make sure it's seamless, not to mention the layer-based stuff it can do. Despite a few annoying quirks it's powerful and it's free, and never having been a Photoshop user I don't have the 'confusing interface' complaints regarding it. Most of my texture work and other digital graphics are done in GIMP. It's also often the best option for color swapping graphics according to a palette so I find it handy there as well. SLADE is good for WAD management though and I use it fairly often for that.

unless it's in there and I've just not been able to find the instruction for it. The only thing I really miss compared to the 'heavyweight' editors is being able to move floor and ceiling heights in 3D mode. Now that it supports Hexen format I probably don't have any need to use a different level editor. I've mostly settled on Eureka for map editing because it's light and unfussy and it works well on both Windows and Linux (SLADE's map editor is kind of unreliable and its Linux support is a bit iffy as well, Doom Builder is too Windows-centric).

Download OpenMPT 1.31