Font/Fount of Information?
I have seen it both ways:
He is a veritable font of information.
He is a veritable fount of information.
The first is referenced by M-W's definition and seems to match the pronunciation I'm used to:
source, fountain (a font of information)
The second seems equally sensible given that 'fount' can be an abbreviation for 'fountain'.
An NGram shows that 'fount' outpaces 'font' in written usage (seemingly in contradiction with the dictionary), but both seem to be pretty widespread.
Are there any reasons to use one over the other, or are they really wholly interchangeable?
Solution 1:
This usage is something of a "stock phrase" with knowledge/wisdom. Historically, fount has always been more common, but as this NGram shows, font is rapidly catching up...
I don't think there's any difference in meaning, or in UK/US spelling preferences. But personally, I've always thought fount here sounds a bit quaint/archaic - perhaps I'm just ahead of my time.
It's worth pointing out that OP's exact phrasing (with the very quaint/archaic use of veritable) simply reflects the fact that all variants are normally used somewhat facetiously.
Solution 2:
From The American Heritage Dictionary comes the following:
font n.
1. A basin for holding baptismal water in a church.
2. A receptacle for holy water; a stoup.
3. The oil reservoir in an oil-burning lamp.
4. An abundant source; a fount: She was a font of wisdom and good sense.
It seems, then, we have a case of potato-potahto. Either word—font or fount—is perfectly appropriate. I happen to prefer "font".
Solution 3:
Are there any reasons to use one over the other, or are they really wholly interchangeable?
The spelling fount survives in poetic diction as a synonym for fountain, and in more general use as a figurative word for "source," as in "fount of wisdom." (Reference: "Handbook of Varieties of English," Kortmann)
So, according to Kortmann's book, it seems these word are not wholly interchangeable and you should use font for the ceremonial "baptismal font."