What synth has your favourite arpeggiator? Whether it’s the versatility, the ease of use, the way it functions, the sounds it makes etc.
Arps are what got me excited when I first tried synths. A good arp and sequencer go a long way in making a synth fun for me.
I really like the minilogue xd arp. I love how musical the an1x arp was, but it was annoying to set up each time. I’m in love with the nord a1 but not too crazy about the arp and I’m not sure why. I love the pro 3 arp.
I love the Bitwig arp for one important (to me) feature: humanize. I find most arps too rigid or predictable sometimes, so sticking humanize on at around 3-5% helps vary the timing and velocity just enough to go beyond the grid and feel ‘played’.
The pro3 arp has a really nice feel to it in a way that’s hard to put put my finger on. Oddly natural.
The hydrasynth arp is intense! Super powerful and deep. I’m really impressed by it.
I’ve only just started digging into the arp on the digitone but it seems like a very useful utility that will surely prove helpful in a lot of situations.
While I like a good, fun arp, I’m not a big user of them in general for the reasons that @craig mentioned. I’ll more often use them to generate ideas than use them in a final recording. These three might become exceptions to that.
The arp on the Micromonsta2 is fantastic! 1-16 steps, each step adjustable to many different behaviors including lowest note, highest note, chord, rest, 2nd/3rd/4th note entered, tie, etc ~ It’s a charming combination of power and ease of use 
The OP-1 arp is my favourite. The extended note modes are incredibly inspiring, and I’ve had whole sessions where I’ve been content with listening to it on its own for an hour or more.
As of recently I really like the ARP on the Keystep Pro.
Mostly just one feature of it.
If you hold down some notes and then press other keys individually they are added to the arp.
You can even add the same notes multiple times in a row. It’s like writing a little sequence on the fly.
Then you can transpose, change octaves, change gate lengths, swing etc; all while the arp is running. You can even move to a different track and the arp keeps playing while you start another.
I guess it’s my favorite arp implementation right now.
In Software: BlueARP eats most other arps for breakfast.
Bonus is that kids eat free!
Honorable mention goes to MIDIsizer MIDIArp for MIDIGal (hardware)
NDLR : LFO on Time divisions, Humanize function, Scales, …
Octatrack, Digitone and Analog 4.
Hydrasynth.
Peak.
MC-303.
What does NDLR stand for?
Noodler for noodling.
It’s not like in French : Note De La Rédaction.
It’s not a Synth, though, it’s a Sequencer.
MC303 \ MC505 hands down
Deepmind (12) has a great ARP with a lot of presets (32). Furthermore, ARP can be sent to MIDI Out, which makes my other synths alive in terms of ARP
MicroFreak also has a nice ARP, which in turn can be turned/saved into a sequence
Similarly, I came here to say I’m very happy with the arpeggiator on the KeyStep 37. I find the pattern mode particularly useful for finding interesting variations on a series of notes. Combined with the strum feature in chord mode things get even more interesting.
StepPolyArp on the iPad is amazing. If you pair it with Drambo and some midi routing, you have a p-lockable arp that puts the OT to shame. Haha.
Monomachine SID arp 
The Volca FM time division knob is really fun for pushing the repetitions into the audio spectrum very quickly.
+1 for the MnM arp
I’m in on the keystep arp. Really simple and good fun to use.
I’ve seen this a few times. What makes the MnM arp special? I’m curious about the love for it.
OT, OP-1 then Pro2.
Now I’m sad inside as only have the OP-1 left 
