Having had both, I’m not going to play that game and suggest something complete different that you didn’t ask about. My choice among your two would the the 120mm. Yes, they will both have color but the 120mm will have less. Also as others have suggestions, you can mask them. Mask them both down to 102mm and you are choosing between an F7.5 and an f10 four inch refractors. The 120 wins again with regard less CA.its still there, but it’s less. I can’t say enough how much the 6” F5 achromat is a one trick pony. Yep, it will be an experience all its own when you take it to a dark site on a summer night, plug in a 2” 30mm wide field eyepiece and start cruise down that highway in the sky called the Milky Way! It will definitely excel there, but that’s the only place it will. You can’t take it downstairs to the sidewalk, garden, or nearby city park for great views of the planets or the moon. Also, having mount had a Synta 6” F5 achromat, once you put a 50mm finder, two inch diagonal, and a heavy eyepiece on their you have a hefty chunk to lug around or mount. Frankly, in your living situation, if you’re really bent on an RFT achromat refractor, the best deal going is an ST120. Its also an F5 but its soooo much smaller and lighter, and color is better controlled, but then, I’m starting to play that other game which I said I wouldn’t. Oh well, as long as I drifted over there, I will say that a 4” F10 achromat is a darn nice do-everything alternative that stays within your budget.