I think RTS would be way easier. Balancing is more or less a matter or planning ahead or doing the math/numbers and weighing them out in a planned format before you commit to it in code. All you'd have to do then is make minor tweaks here and there where one factor is a bit more heavy then where it would seem on paper.
You make it sound to easy imo. The coding aspect may not be that hard but that is only one part of making a RTS. Making a balanced RTS with +20 units, +10 buildings, which could be considered a small RTS, would take many days/months/years to get balanced just right. Unless you're extremely lucky you'll have to be prepared to work hard on getting a balanced game. If a unit just give 2 hitpoints to much in damage it can change everything in the game and make it to hard/easy.

I've always wanted to make a game like Red Alert and I hope to do it someday, but it's such a big project that it's hard to get started with it stay motivated for the whole project.