Good question. Sounds to me like a digital synth that has bread and butter ...or traditional sounds like strings and keys...
I keep leaning toward used, but newer ROMpler...then look into an Alesis Fusion.
Should be cheap and has a lot of (synthy programming) features and they added a new sound set within the last year ot two.
It seems to have had a surge in popularity.
Weird and new tones, I'd say V-Synth, but I don't know what that does to your budget.
Pads, pads, pads. I know it's a hardware forum, but damn if Spectrasonics Atmosphere aint the king of pads.
I have an AN200 and I wouldn't say that it's specialized for pads or even traditional synth tones.
A Korg old EA-1 does great for cheap blippyness and an extra layer of tone.
So again, if you're really concerned with adding extra sounds (presets) in the future then an Access TI (Desktop or even TI Snow) plays back patches of every Access synth...ever
. If you run out of sounds with that....
Check out their site and listen to those tones. http://www.access-music.de/
I come back to this because I think it's better to be able to add new patches/presets than expansion cards as far as longevity and cost is concerned.