Which one is correct?
Correct is a relative concept here. They are giving you different results. If you read the TeXbook then Don Knuth clearly intended to have the input syntax as concise as possible, i.e., I claim for most situations he would maintain that
However, as mentioned they produce different output, because the
the 1 on the p would be placed slightly higher than the 1 on the q. If that bother you than you could trick TeX's rules in thinking there is a superscript by using an empty one, i.e., through
But such a scheme would break down the moment the real superscript would be more complicated so that TeX would need more spreading to avoid super and subscript touching each other. E.g.,
would again fail to get the exactly on the same height, though it is less visible than the first example.
The way for the perfectionist to fix even that (as suggested in a comment from @zunbeltz) is to use
Same kind of corrections could or would be needed in case you superscripts and superscripts + subscripts.
Here are the four examples each with some
postscriptum: personally I find it a little disconcerning if subscripts (or superscripts) change vertical placement in some cases, not so much in the example above but when they appear fairly close to each other e.g., in
The is a way to get the subscripts placed lower by default by changing the font parameters in some math fonts (see TeXbook) but this is also a questionable solution since normally the default drop looks better.