I just renewed and put in three years as the date but haven't picked it up yet-normally, after the two-year you get a three-year- now, my passport was expiring when I first applied so I got a six month extension, now I just applied and stuck in the three-year date- will see when I pick it up in a week.
I would definitely do a three-year application, worst that they would do is give you less- but pretty sure you will get the three-year.
I just did mine last week and due to coronavirus have to go back to pick it up- they don't want people hanging around. Also, it was PACKED with people looking for every kind of extension as no one wants to return to his or her respective coronavirus-infested hell-hole of a birth country (I am from the US and if I were in HK on a tourist visa, would definitely be applying for an extension these days). Was a bit of a feeling of desperation and lots of screaming babies and such (who can sense when their parents are feeling stressed). Hard to even get a seat. Not the usual, more pleasant and efficient experience of the past.