When all else fails, research research research.
Member Ray has several articles about Fertilizers that might help you decide:
First Rays' Free Info
You'll find articles there about plant nutrition so you can find out what each of those chemicals do for you plants, and decide what kind of fertilizer you want accordingly. There are other micro-nutrients besides NPK that are essential to good plant health.
Fertilizers & Plant Nutrition Most fertilizers will list what nutrients are included in the formula.
Most people prefer the balanced fertilizers.
High Nitrogen- mostly leaf growth
High Phosphorus- mostly flowers
Switch between different ones if you want, but balanced fertilizers are going to give you the best of all worlds, they won't keep your plant from growing or flowering- just let them do what they want/need to do.
If you use a fertilizer not intended for orchids, make sure it is urea-free- find one that has nitrate or ammoniacal nitrogen. Being epiphytes, orchids do not have the microbes in soil that break down the urea into a form that they can use.
And DEFINITELY, use Ray's PPM (parts per million) calculator on that page I linked to make sure you aren't overdosing. Generally speaking, 100-150ppm is what you want to shoot for in a general collection.
Or if you want just a plain old tried-and-true recommendation- MSU fertilizer is probably the most popular- it provides complete nutrition for orchids. You can buy it several places online- Ray's version of it on his site is the best deal I've found.