I use mostly the citrus based cleaners now, but opt for mineral spirits or acetone occasionally.

A word about MEK: It is hazardous mostly because of it's flammability and volatility, not its toxicity. Its primary toxic effect is a temporary narcosis, which is why abusers like it. It will get you drunk in no time if used without ventilation. I agree that it's not the right solvent for bike work, there are much more effective products.