My favorite among Händel's oratorios are "Semele" and "Hercules", the most dramatic of all, with a superb orchestra (in special Semele) and real characters, like Dejanira in Hercules.
The Messiah is an extraordinary masterpiece very well known. Jephta is also a beautiful work.
"L'Allegro, Il Penseroso ed il Moderato", "Salomon" are beautiful but more decorative.
La Resurrectione is another wonderful work, in the style of Alessandro Scarlatti, composed in Händel's youth, when he was in Italy.
At last, there is Saul, an oratorio with extraordinary moments (Saul/Samuel, that seems to anticipate Verdi's Don Carlo) but also with weak moments, in special those related to David and Jonathan. It is a pity that Händel did not center the work on Saul's tragedy. The few scenes with Saul are and by far the best of this oratorio.
Regarding the operas I only know a few, and among them I prefer Giulio Cesare and Ariodante, not forgetting the beauty of Acis and Galatea.
I must hear Orlando and Tamerlano. I have been told they are also remarkable.