I have to just mention something form my experience:
I can touch type on my DIY ergo board and use blanks on it, but I can't on a "normal" QWERTY board.
I have tried side printed caps, blank caps and caps with letters printed on the lower part of the keys (KBT Pure backlit caps) and prefer normal caps for most use cases. I have to look now and then to orient my fingers on the board and found keycaps with legends near the top of the keys best for visibility. The side printed were particulary difficult, almost as bad as blanks for me.
My favourites are actually Cherry legends
Of course, if you can touch type it doesn't matter.
Ivan's idea is a great one, so if you really want side-printed buy some blanks and do as he suggested.