When I was in America, it seemed that where either could be used, they would always use upright.  

In Asia and the middle east, it seems they use pendant where ever there is a choice.  I suspect the upright suits freezing climates so that when you drain the system, there is no traped water.  Pendant sprinklers are a little easier to install from below.  Also what installers tend to do in underground carparks in Asia is get rid of the treaded rod and the nut that comes with hanger and bolt the hanger directly to the slab.  This gets an extra inch or so of head room in the installation.   

I like sidewalls

I prefer uprights because the line below serves to protect the head from potential damage. Because the customer will always manage to do the strangest things to their sprinkler systems, so anything we can do to prevent it may help.

Alex Traw
Rainbow Fire Sprinklers
Albany, Oregon
 

With uprights there is a good practice rule that you have to follow (I´m not sure if it is mandatory ¿?) that says that you should align the frame with the pipe to avoid obstruction of the pipe when they go directly on the horizontal pipe, and with pendents there is no need to check this.

Another point is that with pendents there is more possibility of  trapped debris on the sprinkler, when there is and evidence of  dirty pipes on a internal pipe inspection.

I´ve seen a case in a sport goods store where they used the pendent sprinkler deflectors to hang backpacks.

 

Often uprights allow more flexibility in branchline elevation. If the deflector has to be 1" to 12" below deck, you have the whole 11" to work with, whereas with a pendant, you have to fit the pipe, the fitting, and the rest of the sprinkler in the space above.

good day..
if you will compare them, they where actually the same performance provided that you are comparing them with the same characteristic. e.g. k-factor

installing upright or pendent sprinklers will depend on the situation and application you are using them.

for example: you will use it to protect a room with ceiling, you will choose upright? of course not, you will use pendent to protect it and your piping will be on the ceiling space.

yes 3cio is correct, normally upright sprinklers are used in area's that is normally public and have no false ceiling such as carpark, mechanical room and etc. Pendent are used especialy if there's a false ceiling, thus it normally depends upon the architectural plan.