Should buy Intel processor include Spectre and Meltdown bug

Yes and that's scary, hackers most probably found it long time ago, latest "discovery" is just because they had to admit it. It's because of Intel's feature to speed up things and if patched that means some performance loss.
Sep 30, 2013
Even with the patches for Meltdown and Spectre and in the case of AMD the Spectre v2 fix the 8700K is still far ahead in games as would the 8600K also be. That's also true for other single-threaded tasks whereas the 2700X is faster in some multi-threaded ones. And that's including with faster RAM and timings which help both. The 8700K have more overclock head-room and that mostly affect the clock for all cores meaning the 8700K will increase it's multi-core performance and become closer to the 2700X there.

So while I ordered the 8700K early on and waited with a build and later returned those Components I still feel like the 8700K is the better processor.

Then again there's the Spectre-NG stuff with two waves of fixes the last one in August or so and if those will affect performance more who knows.

File performance has definitely been affected but on my SATA SSD with 4K benchmarks it was just 10% and with NVMe drives I think it was like about 1/3 of the performance but of course not all file tasks are done with 4 kilobyte fragmens so real life impact would likely be lower. Then again I don't know how much it affect CPU performance, though I think that was just by some few percents? In games it's have had some impact but not much and not enough to make Ryzen better.

AFAIK the next Intel CPU line-up may be a late 2018 one so it would be some wait. Cascade-lake is a Q4 product and is supposed to be the first one with some hardware modifications against it but as I understand it it's not like they get rid of speculative branch execution altogether but there was some functionality to split things up in whatever way. Whatever that will make it fully immune I don't know. AMD have said Zen2 would had hardware changes for it.
But for both with the 8 new Spectre like attacks which haven't been disclosed what they actually do and haven't been fixed which is known to be a risk for Intel but so far not shown to be one for AMD it seem who knows whatever the new hardware changes will be enough and who knows if more ways of attacking AMD processors can also be found. With Intel having 99% of the server market it's likely more interesting to research and see what one can come up with there but since AMD isn't totally immune who knows what someone may come up with there too. Some of the Spectre-NG stuff also affected ARM processors so it's not only Intel exclusive at-least.

As if though in the real world for most tasks the fixes for the i7 8700K didn't had a terrible impact.
Currently it's definitely insecure but since it's not public HOW it may not be very risky to have one now anyway.

As for the old Meltdown and Spectre bugs antivirus companies has reported more and more code take advantage of them so they are definitely exploited in the wild but an up to date i7 8700K system have fixes for them so .. You're fine there.