So far, I’m indifferent.
I do love symmetry, but every standard/common non-ortho layout is not symmetrical on R2 and R3 (right?). So, I’m not sure yet that I would feel particularly strongly about maintaining symmetry on R5.
Anecdotally, I have all three on one keyboard or another, and I hadn’t thought about it much before this thread.
I do think the case-by-case rationale behind a particularly spacebar length choice seems more appealing to me (v. a universal preference). For example, the HHKB’s spacebar length is to avoid forming a cross at the right edge with the , and . keys; or @djmantis’s use of mods as arrows keys, which is pretty cool.