We really can't answer that question -- either one may be right for you, and your choice will depend on a variety of factors. To help you with your decision, we'll give you some food for thought.
As with any knife purchase, first you should get a clear idea of how it'll be used and how hard you intend to work it. And while it's true that fixed-blade knives can take more of a beating than knives that are "pre-broken in the middle" (folders, that is), there's more to it than that.
Many of the locking mechanisms available on modern folders are plenty strong enough to stand up to rough duty. In addition, you should also take into account a blade's height, thickness, geometry and grind -- the more structurally robust the blade, the more (generally) it'll be able to withstand.
Think about how you plan to carry your knife -- inside a pocket, clipped to a pocket or carried on your belt -- and realize that a knife's weight may influence your choice as much as its physical dimensions. Also, consider that many small fixed-blade knives can be just as pocketable (with the right sheath) as a folder or traditional "slipjoint" pocketknife.
How convenient do you want your knife to be? If you expect to have both hands available when deploying your knife, then most any type of knife (including traditional slipjoints) will work. If not, you'll probably want to go with a fixed-blade model, a one-hand-opening folder or a folder with spring-assisted opening.
Finally, know your local and state laws governing fixed-blade knives and blade length, and choose accordingly.