From my youth, The Heinlein juvenals, Farmer in the Sky, et al.

Also When Worlds Collide, by Wylie & Balmer, which I read 4-5 times cover to cover before I started something else. Go figure why it grabbed me like it did. Also Bradbury and Asimov's Robots. Oddly I didn't read the Foundation series until much later.

More recently, my overall favorite is probably Vinge. I have read everything he has written and love all but the last one, Rainbow's End.

Other, more recent, include early Niven and his collabs with Pournelle. dan Simmons' Hyperion Cantos and the illium/Olympus series

The Forever War, Armor, and The Nights Dawn triolgy are a few more I have liked a lot. ND is pure space opera but again for some raeson it appealed to me.

I have not read much in the last year but talking about it here is likely to get me going again. A disappointment like Rainbow's End will get me stalled for a while but finding something good will set off a frenzy of reading