Oaks are supposedly pretty good at it :)

However like 70% of it (oxygen production) comes from Algae & the sea.

ive got a few favorites. Apple trees are always nice, birch trees are a nice sight if you live up north, and oak trees are pretty nice

It isn't a tree but I really enjoy the cannabis plant.  Some people on the east coast I believe refer to it as trees.

Very bleak if true. The number of O2 producing algae has plummeted in the last 50 years. Maybe we can convert the Sahara into a tropical rain forest (or even an oak tree forest XD).

Pine trees, mainly when they're covered in snow in the winter

Pine, because in my language the name sounds similar to mine. There aren't many pines here though.

Spruce and pine.

The bacon tree.

Olive tree, cherry tree, lemon tree and conifers (when I was a kid I preferred the cypress, now I like almost equally almost all conifers).
Not a proper tree, but I like bamboos, although with the climate change they have become infesting in my garden.

We have only boring trees here so I don't really know. Also, whatever happens to be nice in summer is usually ugly in winter, so there's that too. I'm sure I'd really like some trees, but I'm not familiar enough with them to be able to name any.