I think mallets are really a thing of many many years ago. the positive hit you can give a plastic chisel with a 16 oz hammer is amazing. just more useless stuff to cart around.( I do use a lignum mallet on carvers though)
Not in my workshop they are there on the wall rack ready for use and with the wide head of a mallet you can keep an eye eye on the cutting process and not where the hammer will strike the chisel, Just the way i was taught years ago hard to change old habits
I never look at the handle I'm hitting....after 50 years it's instinctive where to hit.....
When apprenticed I was told...."u get 1 shinging an hour to hit something with a hammer/mallet but 9 shillings an hour knowing where to hit it and how hard.....hahaha...
I worked with a proper Blacksmith for 2 years, man he tought me a lot.....
at 72 with a dicky ticker I can still use a 14lb sledge accurately but tire after a dozen blows.....all good fun.....
Just had a quick glance at my rack:
25mm gets used all the time: I have two, one as a "beater" (cutting socket boxes in plaster board, taking up floor boards (I'm a sparky)) plus a second one for cuting hinge/mortice lock recesses.
1/2" for tidying up mortice lock "pockets".
1/4" for fiddly work.
Plus I have a 1/8" for those awkward jobs.
Realistically, the answer to your question depends upon what work you're doing:
A couple of years ago, making pergolas, my 2" chisel was used all day, every day, and none of the others got a look-in
In my hobby workshop (I mostly use power tools everywhere I can) the 25mm chisel is the one I used the most, and the only one I keep out on the bench with the rest of the set in a drawer. Second most used is a 20mm Narex skew chisel, for trimming off plugs over screw holes etc or effectively as a plane where there isn't space for an actual plane – the skew cut makes it great for paring by hand instead of hitting with a hammer/mallet.