This teacher prefers 2, yet pedants objected to the intrusive adverb, be it in the infinitive or not. What was the reason for this supposed rule ? That breaking it makes for misunderstanding, or that the result looks or sounds ugly?
Two examples of how nuance, emphasis, meaning are changed by the position of the adverb:
" I happily overestimate" and "I overestimate happily" convey different meanings; the nuance of the first is that overestimating ,itself, is something I am proud of, and certainly happy about, whereas "I overestimate happily" conveys no more than that I'm happy while I'm doing it.
The intrusive adverb brings emphasis: "I boldly go" is drawing attention to me as ' I am bold and I am going', emphasising my boldness; but " I go boldly" lessens that as "I am going and in a bold manner".
Sometimes it just sounds better to have the adverb in the middle, it 'scans' better, sometimes it doesn't
And 'Do you come here often?' has been the cliched polite introduction to small talk for a very long time. It has not been 'Do you often come here?', perhaps because that puts too much emphasis on 'you' and 'often', as though the enquiry was about 'your' eccentric or odd behaviour in attending frequently!