One doesn't have to observe every object in the heavens to have a favorite or a favorite by type. Since there is now an amateur astronomer who owns a 70-inch aperture, it is a physical impossibility for an observer to see every deep-sky object that is visible with such a telescope in the span of a human lifetime.
I have observed from both hemispheres. If I had to pick a single DSO that is the most interesting to observe, it would be the Large Magellanic Cloud, which contains the gigantic Tarantula Nebula (also known as NGC 2070 or 30 Doradus) and numerous open clusters, stellar associations, and globular clusters. I spent several hours logging objects within the LMC with a 22" Starmaster Dob.
IMO, NGC 5139 (Omega Centauri) is the most spectacular DSO visually, with NGC 104 (47 Tucanae), which has a unique inner core, coming in second. Some observers put NGC 104 first.
NGC 3372 (the Eta Carinae Nebula) was the most impressive nebula that I've ever viewed.
My favorite open cluster, NGC 3532 (the Wishing Well Cluster), also resides in the southern hemisphere sky.
Sic itur ad astra!
Chance favors the prepared mind.
A man is a small thing, and the night is very large and full of wonders.