I have to say I just love programming the Elektrons. With the different voices (or tracks) being so immediately accessible and the built in brilliant sequencer, toying with them are just bliss.
But nevermind the Elektrons - which is your favorite piece of gear to program, and why? 
Hmm, outside of Elektron gear Iād say probably a Virus. I bought a Virus A again a couple years back and although I eventually sold it to help get an A4 it was funny how I remembered the menu structure etc. perfectly after a 10 eyar interval. I might pick up a virus KC or something if I find a good dal on one, still fond of that sound and of course the front panel is great.
Strangely I also liked my Ensoniq ASR-X even though it only has 2 encoders and a bunch of buttonsā¦but maybe iām just being nostalgic about the sound.
Besides MnM (and it is really good and challenging - like some digital modular monster), I really enjoy making noises on Waldorf Q (actually, rack, but the differences between key model and my rack are just a few, excluding number of encoders). That synth has so many possibilities, especially regarding modulation options. Route envelope 3 to LFO 3 to wavetable Alt1, add some tasty sub, FM, and you just used only one of the first two oscillators (the third cannot use wavetables). Add some tasty modulation of filter routing (!), etc, etcā¦ In fact, my first synth was Moog Prodigy (waaaay back), and it was wonderful 'cause everything you did on a panel resulted in wonderful sound. The Q gives me that feelingā¦
I love programming Arturia Minibrute. I have stacks of analog monos - Little Phatty, DSI evolver, BSII, the list goes on and on. But when I just want to explore a synth and twist some knobs I think the simplicity of the MiniBrute is what makes it so much fun to tweak.
The simplicy of No screen, no presets, one oscillator, no hidden functions makes every tweak very immediate and satisfying. You have to coerce everything out of it yourself.
Yes, there are thousands of synths that are more capable than the Minibrute (and I own several of those too) but Iāve yet to find one as much a joy to program!
I still love synths that give me everything on the control panel at once. The closest Iāve come to that on a modern synth is the Prophet 12 but it still canāt compare to my Jupiter 6 (with Europa mod). I just love hitting the āManualā button and then tweaking the sliders until something magical comes out. Instant inspiration. Iām hoping the Moog Sub 37 is going to appeal to me in the same way.
The only Elektron box that gets me close to that is the MD. I love simple instruments and relatively fixed UIs. I can remember where everything is on the Effects and Routing pages so it becomes second nature to use. I have to think too much with the A4.
Virus TI and microwave XT are synths i get really lost in and never get frustrated or bored with.
the reasons are pretty simple. i never stop coming up with interesting sounds. they are very both very engaging and the XT in particular can be very unpredictable, which i love. the sound on both is very pleasing to my ears. the menus are not overwhelming to me and in some ways make it more fun because they force me to hear a sound i want to make in my head before i try to program it. when i have nothing but knobs i get a little twist happy. if i could have only one it would probably be the virus though.
as far as samplersā¦ octatrack forever.
OP-1 
With only four knobs and buttons , it is very fast to make sounds.
Op-1
Doepfer ms-404
sy77/sy99
the modulars of fm synthesis
Virus TI for deep, satisfying programming.
Micromac for raw tweakery and the joy of knowing it canāt be saved.
Sweet, this is interesting. Lots of love for the Virus TI. I got to try one a couple of days ago, but only for a few minutes, seemed very deep indeed.
I never really got into my XT, for some reason. Loved the sound of it, but never liked programming it, despite the many knobs.
How deep is the OP-1 though? From the SonicState review it just seems like the synthesis options are quite limited, like there isnāt a whole lot to do with the different synthesis methods.
OP-1
PolyEvolver Keyboard
Yes. And no.
Currently there are eleven engines including the samplers and drum synth, with a twelfth coming, and dbox/the coming 12th based off it will be the only ones with a built-in filter (normally you need to use the single effect slot for Punch or Nitro), for example. but considering the fact that you can play to Tape, then lift that audio and drop it into a sampler (bearing in mind the time limits of the sampler youāre using), itās strength is not the raw power of each sound generator but in manipulating the sounds you can create.
Itās not a poor manās Virus 
Roland MKS-30 with the PG200ā¦
Big Virus fan here. Its my deserted island synth for sure. For simple fun, I love the Moog minitaur over my Voyager, strange i knowā¦ I tend to run it through the OT FXs to get the bass wide and nice.
Yes. And no.
Currently there are eleven engines including the samplers and drum synth, with a twelfth coming, and dbox/the coming 12th based off it will be the only ones with a built-in filter (normally you need to use the single effect slot for Punch or Nitro), for example. but considering the fact that you can play to Tape, then lift that audio and drop it into a sampler (bearing in mind the time limits of the sampler youāre using), itās strength is not the raw power of each sound generator but in manipulating the sounds you can create.
Itās not a poor manās Virus [/quote]
I think KrisM nailed it there. Very similar in spirit to the Octatrack, except of course the OT doesnāt even have a sound generator - just sample playback. Thus not a shocker that quite a few OT owners are also OP-1 owners.
The OP-1 seems to be designed to give you just enough tweakability to customize your sounds to some extent, though not as deeply as a Nord Modular G2, Virus T1, Reaktor, or whatever - with the focus on encouraging you to spend more time making actual music and less time nerding out on āultimate patch creationā.
The easy tweakability factor is one reason I got a Microbrute too - twist a few knobs or whatever, and go!
With the Elektrons, the MD without a doubt.
Iām also with Anigbrowl with regards to the Virus, just love that thing!
Not a synth/sampler, but the Cirklon is sooooooooo much fun to program & dick with! If only I could get Sequentix to do a hybrid with Elektron, ahhhh one can dream 
I like shit to be simple, so: Moog Voyager and Juno-60 are my favorites to āprogramā. In fact I program for a living, so I donāt want to āprogramā when I play synths - I want it to be as easy as possible to dial-up something interesting, so yeah, Moog and Junoā¦
Roland MC202, something always happens even after all these years, failing that Iād say either of the Nord Drums (if they count).
Quick and dirtyā¦