Actually, Ryzen prefers higher speed DDR4 with low CAS latency for best performance, though ideally the memory die should be Samsung B-Die (so you'd be limited to G.Skill Trident Z and Ripjaws V, specifically those with a frequency of around 3200 Mhz with a latency of 14).
Anyways, if you plan to keep your CPU for a long time, the fact that you would need to replace your motherboard for Intel CPUs is moot anyways, as after 3-4 years I imagine even AMD would put out a new socket.
Now, Intel CPUs remain superior for gaming, and the Meltdown patch has little impact gaming (but it's a valid concern to have). I'd say it's best to look at what you will do with the computer. If you plan to edit videos, then AMD CPUs are better, but if you plan to only game, Intel CPUs would be better, as the 8700k is right now unequaled. Budget-wise, AMD has cheaper motherboards right now (as only Z370 motherboards are avaialble for Coffee Lake currently), but Intel CPUs are less choosy as far as ram go (you can go with a 2666 Mhz one and it won't perform much differently than a 3200 Mhz one), and ram prices are stupidly expensive right now.
Anyways, for an estimated budget of $1500, I would look at an i5-8400/i5-8600k (ideally the latter, as it can be overclocked for better longevity) or a Ryzen 1600/Ryzen 1700.