Before anyone jumps to conclusions, please hear me out first. I have read another thread in here that deals with a similar subject, but does not quite go into details as I would like it to do. I also read an article here: http://www.pcgamer.com/what-you-need-to-know-about-cryptocurrency-mining/  and it seems to contradict some of the stuff stated in that other thread. That is why I want to outline my main points of concern in the hopes of clarifying the issue for me.

 In the above referenced article, it seems that a PC rig with 6 RX Vega 64 video cards would be able to produce just below the level of the Antminer S9, with a cost just below the $5,000 mark. While the S9 is well over $5,000 these days.  The thread that I read in here a few claimed that a PC would not be able to work for Bitcoin, but that it would be best to do altcoin with a PC. And another good reason for mining altcoin would be the resale value of video cards.  So my questions are as follows:

Are GPU rigs capable of bitcoin mining or not? And are they not capable comparable work? Do GPUs go bad faster than ASICs?

If GPUs can be sold after a couple of years, would this not be a better incentive for using a PC? Sure ASICs would save space, but does the resale value stay up? I am assuming you can resale a video card for about 50% its value after a year or two. But assuming you can only make a 1/3 the cost, you only have to spend 2/3 the amount on a new rig, because video cards tend to stay around the same price range. But what is the resale value of an ASIC? Is it at least 1/3?

If someone can enlighten me as to what would be the best investment. I have been looking into this, but it is hard with all the information out there. Also, I read on another site that you can mine both bitcoin and litecoin on the same machine, with two instances of some application. Not sure if that was in reference to ASICs or PC rigs. And they did not specify if this would cause poor performance on either of the mining instances.