I’ve only recently gotten into the midi sequencing capabilities of the Digitakt, but I think it’s the most fun I’ve ever had with a sequencer.
Most people in this thread (and in others like it) are using and recommending high-powered synths, but what I most recently had fun with is the Ploytec PL2.
http://www.ploytec.com/pl2/
As it needs a dedicated controller, it’s a perfect fit with the Digitakt sending CCs to it. I’m seriously thinking about investing in a few more of them and running mono synths almost exclusively.
There’s also an older series of synths by Yamaha that are essentially midi modules. They run 16 individual midi tracks on board, and obviously all of them can be sequenced through the one midi cable in. In the past I used the Yamaha mu 10, but right now I’m using the Yamaha mu 50 and really liking the results with the onboard effects. Yes, it’s vintage, and a lot of it is generic sound (I think all these modules run on PCM sample playback) but with a little bit of editing the parameters you can get some wild sounds. The mu50 I’m using uses the general midi Soundset, the XG midi Soundset, and the Turbo 300 sound set.
All the devices I listed can be bought for under $100. At some point I’ll upgrade my synth set, but for the time being I’m having a ridiculous amount of fun using these limited tools.
Did I mention using the Digitakt to sequence my Yamaha U1 up right? It has the 1997 disklavier add-on, so the piano sports midi in and out. It’s a little ridiculous to sequence an acoustic piano like this.
Overall I’d say that the high power of the digitakt sequencer means that it works incredibly well even with lower-powered synths. Loving it so far.