For example, if you have a cruiser style motorcycle then an open face maybe what you would choose, perhaps with shades and a bandana scarf over the lower part of your face (it stops you eating flies).
BMW GS? No problem, you need an adventure style helmet to look the part.
Perhaps you are a race fan and would like to wear a replica lid; most racers have some great looking designs. Even if you have no clue who they are, we remember the Shinya Nakano helmet, with the two cartoon eyes above the visor. There is an AGV K3 with a similar design, the Tartaruga. Some followers, especially those of Valentino Rossi collect the designs, which he changes almost by race or test session - an expensive hobby!

You should go for a helmet that fits your head the best. Comfort and safety go hand in hand here and we have always said at My Moto that it is better to get a cheaper helmet that fits rather than an expensive one that doesn't!
There have been some recent innovations, like the inner sun visor that can be flipped away in an instant and the flip front style. Only some can be worn up, (look for the 'P/J' lettering inside, near the E mark,  if it says 'P' then it has been tested only as a closed face and must be worn while riding as such (the P/J labelled helmets have a lock in the open position).