Audiobus: Use your music apps together.
What is Audiobus? — Audiobus is an award-winning music app for iPhone and iPad which lets you use your other music apps together. Chain effects on your favourite synth, run the output of apps or Audio Units into an app like GarageBand or Loopy, or select a different audio interface output for each app. Route MIDI between apps — drive a synth from a MIDI sequencer, or add an arpeggiator to your MIDI keyboard — or sync with your external MIDI gear. And control your entire setup from a MIDI controller.Download on the App Store
Audiobus is the app that makes the rest of your setup better.
Recommend an AUv3 synth, stable, modern, good
I need a synth that "just works" and sounds good without a lot of fuss and muss. I've been working with Synth One, but it keeps crashing. So first requirement = stability. Second requirement = total modern -- i.e. plays nice with AB, AUM, and all the interactive features and parameter controls. Supported by a team that cares about updates. Polyphonic (I'm a piano player).
Sounds? Analog retro is always fun. So is DX digital. But I prefer wave-table synthesis for richness and variety. I prefer patches that sound good out of the box, though I know how to tweak if necessary. I don't need a drum machine.
FWIW, I started creating sounds on synths with the DX7 in the late 80s, and a long list of analogs, then digital-analogs (I still own my Alesis ION and a vintage TX 802). Then soft synths ACE, Zebra, Diva, Alchemy (before Apple bought it). Actually my first experience was an original Buchla, patch cords and all.
Of course I read all the "best" threads here, which are great. I'm ready for specific suggestions.