That's a doozy of a question!
I've used both options and I have my opinions on both.
Pie: requires some IT experience and/or patience to learn how to modify the image to do what you want. If you want to customize it at all, you'll probably need to learn how to SSH, navigate through Linux. I found it fairly easy to modify the things I needed to, but I could understand if it causes novice users some grief. I am using it for a vertical build - you can see the post where I layout the steps for my Pi here:
http://forum.arcadecontrols.com/index.php/topic,161128.msg1702989.html#msg1702989It was an easy build. One annoying thing, that I didn't have to deal with since it was a single game build, is that I don't like the option to modify game settings at launch. Not sure how to get rid of that.
PC: Also requires some IT experience, but it's easier to find support when you run into a problem. You get a whole plethora of front end options.... almost too many. Doesn't take a high end PC for many of the front ends. The failure rate on PC's is a little scary to me. I've had several fail and it requires a rebuild and re-install of the OS. I may swap my Galaga cabinets PC out for a 60-n-1 or something when it finally bites it.
The other option you didn't mention was using a Jamma board and a all-in-one unit like a Pandoras box. Check it out. It's probably the easiest solution of all. My kids use an Arcade1up and a 60-n-1 board and it works great for them.
If time is available, my suggestion for you is to try a pie. It's cheap and easy to experiment with. Also try to find a free or very inexpensive PC and give that a whirl. Watch some videos on the all-in-one boards.