Filters -- don't get me started ;-). Had a Doepfer A-121 first and still have it. Does it all without much coloring.
Polaris - very versatile and a good and only one in a small rack. Selling mine was kinda dumb.
Most fav'd ones... Hard to say. Recently I use Blades a lot, for its versatility and dual use as a VCO. As far as character, I love my Doepfer Wasp and Bastl Cinnamon. Also, Steve's MS-22. Font is a good and versatile one.
On a more neutral perspective, Ripples is great. Toying with the idea of having a stereo version in my sum. Joranalogue Filter 8 is clean and precise and a 8-phase oscillator, too.
As for specialties, the Klangbau Köln Twin Peak Resonator is great, almost an instrument in itself. King of pings!
And last but not least, the mighty Serge Resonant Equalizer. Not a filter but a fixed filter bank - and a very opinionated one at that! Squelchy squealy feedback goodness, as those distorting filter bands interact which each other. Can it get any better?
Still interested to get my hands on a Three Sisters, North Coast Coiler and Leap Frog, as well as Moon Phase and Linnaeus (not so much the Morpheus). Keep hearing great things about IMÁGENES and Inertia as well as Neutron Flux (which seems to be deeep).
Right, filters. Don't get me started.
BTW, who needs oscillators when you can have filters that oscillate?
I should build a rack devoid of oscs.