What is generally the best and/or most useful heightmapping tool?

[Colesy]

Hello folks.

I'm brand new to this community, if we aren't counting some anonymous lurking here and there. I've taken a look at RobA's thread titled "List of Mapping Software" and I've briefly checked out a number of the links associated with the tools. Now, I've never really done any serious mapping of really any kind, so truth be told I didn't really have an idea of what I was looking for. I've toyed around a bit with World Machine but at the moment, I am almost completely inept in that program. That said, I thought I'd search around and maybe try something new, perhaps with a little less of a learning curve.

So here's the deal. I'm trying to make a heightmap based off of one of my (wildly incomplete) maps that I've had sitting on my computer for ages. Take a look at it (and do please try to refrain from pointing out that the mountain ranges look like a stick-figure cat):


First I decided to use the parchment-looking image as a reference in World Machine, but I've been struggling trying to match the terrain to the original image. After I gave up on that, I decided I might try to hand paint the entire heightmap. Here's how far I got until I asked myself if there was any better way of doing this:


All I want is to be able to maintain the base shape and add in some terrain features that won't take up too much space, because I am trying to use this for something that is gonna require a lot of flat ground, though I don't want to compromise on detail. In the end, it needs to be 8-bit and have a large resolution. So for this particular scenario, does anybody have any recommendations for which tool might suit me best here? I'm sure there's a lot of variables that can go into this question but, what does everyone think is the best and/or most useful heightmapping tool in general? If such a thing even exists. Anyway, thanks folks.

By the way, if anybody would like to see the end product (if that times ever comes) then let me know. Perhaps I can share it as my first WIP/Critique thread.