for half life 1 i really like surface tension!! lets u use basically ur whole arsenal with pretty balanced fights (i'd say forget about freeman gets a bit over the top with the alien spam)
for half life 2 it's a hard pick between ravenholm, highway 17 and nova prospekt, but i think i like ravenholm's execution the most
for half life alyx arms race is definitely my favourite for all the combine fights but captivity is also really good!!