I've got 2 Krink kits.  One is a 7.62 and the other is a 5.45.  The 5.45 is a sidefolder and the 7.62 is an underfolder.  Should I get the 7.62 built up as a sidefolder also?  I've heard that this is way more comfortable to shoot.

The decision is totally up to you slammer. Underfolders are cool looking and do a great job at cutting down on the overall length of an AK, but Underfolders get loose. There's nothing you can do about it, it just happens. They also off next to no cheekweld.

If you are a collector then naturally you'd want to restore the gun back to original form, but if you are building a shooter (like me) a side folder offers a better more solid rear stock with a good cheekweld.