I'd say I'm more comfortable with the current editor. May be because I reaaaally know it at this point, but I just like it compared to the older editors.
That said, if you could figure out what makes the TGEA editor so comfy to you, that's the sort of thing that makes for good notes on improving things going forward. An editor you can feel comfortable working with is really important.
I was thinking about that and, I think, it kinda comes down to them feeling more "straight forward" to work with. Fewer buttons to push. Fewer places to have to poke around for things. I think there was something "elegant" about the TGE/TGEA editors.
Also, I like the "feel" of the terrain editor more, for some reason. I just can't get comfortable with T3D's terrain editing.
My biggest beef with T3D has to be the weird way it handles terrain materials. The approach taken by, well in my experience, most every other game engine I've worked with, is more straight forward. Among my favorites are where you create a new material, assign your diffuse texture, normal map, spec map, etc. Then, each element has a slider with a real-time update view to see what it looks like. Get it where you want it, click 'Save', and you're done. It can take seconds to get a perfect looking basic material, no fussing with decimal places. A few also have vertex color blending, so you can colorize the terrain in spots, to add variation or change the overall look of it (I think Blizzard started doing this in WoW, too, either this expansion or the last one).
T3D's approach feels very convoluted to me, by comparison, like it's off in left field. It's the only terrain material editor I've ever seen that works the way it does. You have to make sure you have good color/brightness balance for diffuse and detail textures. Then you have to fidget with numbers at the decimal level 'til you find the right blend. Then you have to make sure your macro detail texture is well balanced against the normal detail and the diffuse, or things get too bright, or too dark; this also requires fussing with extremely small numbers. Then there's making sure the normal texture is "just right", which also involves messing with really small numbers, to not get really bizarre "warping" effects on the surface (I've never seen this phenomenon happen in any other terrain editor with normal maps). I'm sure there's a method to its madness, I've just never been able to wrap my head around it. It always feels like I'm fighting with it to get results I could have in seconds in other editors.
If there were a genie in a bottle granting me a wish, it would be for a reworking of the terrain material editor to be more intuitive with better visual feedback.
Aside from that, I'd like to see the height editing tools standardized a bit, too. Those also work very differently from most other engines. T3D is the only editor I've used where "flatten terrain" continuously updates the "set height" as you move the brush, causing it to rise and lower as you move around. The standard flatten tool works where it gets the height under your mouse cursor when you first click, locks in at that value, and then adjusts the terrain to that elevation as you move around, until you let go of the mouse button.
As for TGE/TGEA's set up... I think I like their terrain texturing approach better simply because they are much more straight forward. Pick the diffuse texture, pick the detail texture, done. You get results that just look good without having to fuss with them extensively. The lack of options works better in their case lol. However, expanding on them, I'd *personally* have liked to see the terrain material workflow taken in a different direction.
To give an example, Esenthel has one of the most intuitive and straight-forward terrain material editors I've ever seen or used. Here's a demo of it in action.
You can see how straight-forward and intuitive it is, with great visual feedback, etc. I'd suggest watching the whole vid, as it shows off a variety of tools that, I think, would be phenomenal in T3D. Would love to see something more along those lines in T3D
My two cents.