@AT Depends really on your budget.
You can use any synth with Midi in port.
The Digitakt has 8 dedicated Midi tracks. This was one of the primary reasons I bought it.
So you can basically sequence any synth you want that has MIDI IN. Which is basically everything these days.
I have a Novation Circuit and able to sequence the two synth tracks from the Digitakt.
I have a Behringer Crave, which is an analog mono synth. I can sequence that one.
And since yesterday I have gotten hold of Hydra Synth desktop, which I can now sequence from my Digitakt as well.
The Hydra synth is an awesome polyphonic synth!