For saving synth presets in a single synth pedal, your options are:
- Markbass Super Synth
- Chunk Systems Octavius Squeezer
- Korg G5
- Akai Deep Impact
I have the Markbass and like it, but it's not without its problems, mainly not easily editable without a computer. You can't have octave and synth together, but the synth section is big sounding - I don't think you would need to. Has its own 12v power supply.
The Octavius Squeezer is reportedly difficult to program, and to my ears, sounds thin because it only has one oscillator.
The Korg G5 is an analog synth pedal - waveshaper with a filter. It's big and doesn't do really clean synth sounds well. It's discontinued and aging, but you can find them in the classifieds.
Akai Deep Impact is digital, does clean sounds, but is also discontinued and expensive second-hand.
If you want a new pedal, I think the Markbass is the one to go for. But be prepared to adapt your playing style (as you probably did with your Line 6) and tweak the sounds at home on your computer. When I can afford it, I'll probably move to a Deep Impact, unless another pedal comes along first (Source Audio are working on one).
The other route many players take is two or three separate pedals combined - octave into fuzz into envelope filter. Each pedal is useful by itself, but can be tuned to some great synth sounds.