While for certain kinds of things the choice of which form of IP protection to seek is obvious, it's not too hard to think of examples where there could be more than one possibility. To illustrate this point, I would like to use for an example nothing less than a humble bottle.
So, you have a better bottle. That is, it is a bottle that works better as a bottle than any bottle before, like this patented squeezable beverage bottle. Since it might be likely that your better bottle can be reverse engineered, you will probably want to file for a utility patent to protect the functionality of your invention.
But what about a design patent? Well, if you have a new design for a better looking bottle, you may want to protect that, and that's when the protection of a design patent could come into play, just as in this perfume bottle design.
Now, what if you want to use your bottle as a distinctive element in an advertising campaign for a new brand of drink? You want the design of that bottle to distinguish your brand from competitors' products, and so have created a unique special shape for your bottle. To protect that look from being used for competitors' brands, you will want to try to get trademark protection for your bottle's design.
The Original SculptureFinally, could you copyright a bottle? With apologies to Andy Warhol, if your bottle is a work of art you might want to try. Or, to look at this question from the flip side, if your sculpture is appropriated to serve as a bottle without your permission, you might find yourself suing for infringement, as in this case (this link only works in the library, it is to the Boston Globe article: "Cologne Bottle Gives Artist Sense of Deja Vu;" Boston Globe, January 30, 2009, page B.2. This article may also be accessible on the Globe's website: www.boston.com).
The Alleged InfringerWell, after all this, suppose that more than one form of IP protection is available for your bottle. It's time to shift into business person mode, and think about what factors you would use in making your choice(s). Next time, the final factors...