How long are you going to stay in your house? That's the real question. Just about all the security systems cost the same, but the longer you stay the better it is to pay up front. If you're not going to monitor then just get some stickers and call it a day. If you're going to monitor you have to realize that cutting the cable/phone line is going to stop it anyway (unless you pay for cell).
Here's the dirty secret: It takes .4-90 seconds for remote response from central station, but an average of 20 minutes for the cops to get there. It takes a cop 20 minutes to drive from one side of my town to the other. Sorry, a theif is not going to wait that long.
As far as equipment, THEY ARE ALL THE SAME

! The thing that matters is who installs the equipment. Wireless can work, but a lot of false alarms are from wireless equipment improperly installed. Just remember that if you go with ADT and some of the others you DO NOT OWN THE EQUIPMENT and can't change monitoring/service companies after the initial period is expired. They have special chips that only work with proprietary equipment. Make sure you are specific that you want any and all programming lockout codes to be provided at the time of installation.