If you can find a rare 180 or 195, and know how to use an adjustable manual camera, those would definitely be the best, but they will not come cheap, even to this day in the digital era.
For versatility and performance at a lower price, I would want one of the folding automatic ColorPack models with the triplet lens and a choice of two apertures for each of four film speeds.
The general-market models fitting this description are: (Automatic...) 100, 230, 240, 250, 340, 350, 360, 440, and 450.
You'll need to power these with the right batteries. #531 and 532 batteries have been discontinued for two decades now, but an amazing number of these batteries still work! Powering up with a new battery is a little more complicated. I have had luck using rubber bands and tape to connect the flat faces of the common 123 lithium battery to power 3-volt models. 4.5 volt models are a little more complicated, with some using the battery holder from dollar-store LED lights to hold three AAA batteries to get 4.5 volts.
You will need to cut off or bend back the pressure clips on the film door of any of these cameras as the pressure clips, as-is from the factory, will push on the plastic back of the modern Fuji film pack and stop you from pulling the tabs.
Another option would be the rigid-body color-capable cameras such as the Super Shooter. One big advantage is that they use two AA alkaline batteries - still easily procured as of August 2014. Their plastic triplet lenses are still sharp enough that the sharpness of the picture is limited by the instant film itself. I do find that the smaller rollers on these is not quite as reliable as on the folding models, however.
