Experience has shown that failing to adequately protect your iPhone will most likely lead to it becoming damaged to the point that it is either functionally limited, or in the worst case scenario totally destroyed. Depending upon your lifestyle, adequate protection can simply be installing your phone in a relatively cheap iPhone case. For people who lead a relatively active lifestyle that includes plenty of travel, sporting activities and active use of their iPhone a more rugged and therefore more expensive iPhone case is probably warranted.
The selection of iPhone cases available luxury iphone case is enormous and if you let it the choices can be overwhelming. Therefore, before purchasing a case stop and have a think about the types of stresses that you will be subjecting your phone to. Is your day mostly commuting in a vehicle and working in an office environment? If so, a dual-case made of silicone and plastic that is waterproof to a depth of 25 meters is probably overkill for you. Select a case in the $25 to $35 range that snugly encases your iPhone in either a plastic or silicone case.
If however, you spend much of your time working in an outdoor environment, or you work around water or other environments that could be potentially damaging to your iPhone then you should consider a stronger case that has been designed to protect your phone in extreme situations. Expect to pay in the region of $50 to $100+ for such a case.
No matter what style of case you purchase it is highly recommended that you also purchase a screen protector to go with it (check to make sure your chosen case does not come with a free one as many do). Screen protectors have been designed to protect the delicate touch screen of your iPhone and are required regardless of the lifestyle that you lead. A touch screen can just as easily be broken by the keys in your bag as it can by heavy machinery on a construction site.
The selection of an iPhone case is really a personal decision that is dependent upon the stresses and strains that you are going to subject your iPhone to. For relatively benign environments a simple, well made case will suffice (although if a more rugged case suits your style then go for it!). For more stressful environments you should really invest in a sturdier case that offers more protection. In all situations it is highly recommended that you also purchase a screen protector.