I have used Frontline spray for years and years, before most people knew about it. I used to have to buy it directly from Merial.
Don't get a big bottle. A small bottle will last for years. I have Lady and two cats and I usually have to throw mine out when the date expires.
Frontline Spray
The best way to apply it is to saturate a cosmetic puff (not cotton ball - too absorbent) and rub it on. I use half the number of pumps suggested by weight and it is plenty.