neoncube
I'd just go for a simple "choose which learning (or revision) system you want" for each session.
And I'd like it to be set by me for each course until I changed it.
So in practice I might go for pairs first, then words, then finally typing (as long as it isn't a long sentence).
If that makes sense.
PS
On MemRise I set one of the three systems (for everyone) for each course, based on the contents.
PPS
Actually, I would prefer this as a default and then users could change it if they really wanted to.
On most courses where "one word" answers were needed to a longer definition, then the one word would be typing, but the "definition" would be chosen from 4 or 6 alternative boxes.
So two systems applied to one course. That is the advantage of having levels for pairs of answers.
In addition, on some courses (not as extreme as mentioned just above) I would create a duplicate set of levels, where the first set was "no typing" (matching say) then the second set would be tested by selecting "words" or even typing) for people who had progressed from NT.