I have been using this:
KVR: SynthMaster by KV331 Audio - Synth (Semi Modular) VST Plugin, Audio Units Plugin and AAX Plugin What I like about it is you get a nice range of sounds.
What I don't like about it is you get a nice range of sounds. I will spend hours looking for the right sound. It also lets you do a lot of tweaks. It s not a bad synth for the money.
+1 . . . and the preset browser does get upgraded and improved. You can also start out with a free version of the simplified-controls Free Player or the inexpensive paid-for Player (more presets). A SynthMaster-SynthMaster1 combination is pretty monstrous.
If you remain patient, Air Music Tech Hybrid3 and/or Xpand!2 will either be offered for free or for $1 at some point by somebody on line. You will then also qualify for their AIEP3 "complete"* upgrade for $75 which will contain enough quality stuff and presets to keep you busy for months and happy for years. I absolutely love the way after-touch has been programmed into the newer pad patches in Hybrid3 (not that you can't do this with scads of other synths, but it appears to be a tasteful programming approach in Hybrid3). Hybrid3 sounds good, is well-featured, and is worth the MSRP but, once you realize that it is often offered for free or $1, it's difficult to justify paying full/street price for it. Be patient---it will come to you. Get on the mailing lists from PluginBoutique, AudioDeluxe, KVR and Don'tCrack.
If you're impatient for something, Xpand!2 is currently available for $20 (but, again, remember: from time to time it's offered for $1 or free):
Virtual Instruments / Xpand 2 - Audio Plug-ins Store - DontCrack
There's always Synth1:
Synth 1: 25000 collected patches
Speaking of low CPU: A front-runner in that category would be Titan2 but it doesn't often go on sale, and it only comes with 12,800 presets.
Paj
8^)
* the "complete" upgrade does not yet include the newer versions of Loom and Vacuum, Boom, or Ignite. IMHO, still one of the best VST bargains on Earth.