The rainbows will be easier. Less fighting. I wouldn't use the softened water. It adds salt. I have a rainbow tank with 8.3 pH and really high KH and GH. The rainbows are easy. You can put other fish with them also. I don't know if neons will be too happy in your water. I've found some fish do just fine and others kind of fade away. They don't get noticeably sick, they just kind of die off little by little. Serpaes have done great and I'm trying a school of tiger barbs (13) now. They seem to be doing really well also.
I've had (and still have) African cichlids. They are gorgeous, but can be kind of mean. Every now and then I come home to a beat up or dead cichlid. It is usually many months between murders, but they still happen. I have all males now, so that seems a little better. They are still more challenging.
Here's a pic of my tank. Very blurry, but you get the idea.
Here's another picture from about a year ago (before the tiger barbs).
Have fun creating your new tank! You can do a lot with it, even with the high pH. And it is a whole lot easier to work with the water you have, than it is to change it and have to deal with changing it for every water change.
Lisa