I feel like I should start a new thread, as there actually is no useful information on the lounges in Changi Airport.

Anyway, if you are flying oneworld: Apparently QF is the only one that is nice (CX just uses one operated by dnata called Skyview. Nothing nice about that). However, that is only from afternoon onward, so if you have an AM departure it doesn't work. I didn't visit the MH lounge in terminal 2 but it doesn't seem like anything special either.

If you have priority pass, the Plaza Premium Lounge in T1 is the best. It has a nice selection of cold foods (like salad) and also 4 choices (from 11am to 11pm) for made-to-order food: laksa (didn't try), tamaki roll and udon (tamaki rolls are handrolls and nice, udon isn't up to CX standards in their noodle bar), made to order breakfast (including eggs how you want them) and hainan chicken bento set.
The shower is decent, with a full-sized towel, and a rainfall-ish showerhead (just a large showerhead). There weren't many people in there and seating was a darker, quiet mood.

I didn't bother visiting the Skyview. Wellness is relatively dingy and dark, as it is on the lower section (Skyview at least has windows. But the Burger King has just as good a view).

My conclusion is that the only nice lounges in Changi are the SQ ones, and you cannot get in without flying SQ.