Remember one golden rule - Impulse Buy usually turned out to be costly and ruin your airsoft experience
First try out various models by asking people at an event.
Narrow down which one you like
Look for specs, cost, upgrade possibility, spare parts availability, mag availability etc.
Check the doctor's corner to check if thread on your chosen gun pop up often (usually a good indication of the general quality of the build)
Read reviews if available
Then, you can buy without worrying about making a bad decision.
Best of luck in choosing your aeg.