This would depend on how many acne scars you have and their type. If you have a few acne scars and they have shallow shoulders, collagen might be a good answer.
Stretch the skin between the scar. If it flattens out, then Collagen might be a good choice. It is the cheapest option, since a 1/2 cc should run you about $125. The results last for about 9 months to a year.
Unlike collagen for other areas, collagen for scars is to under muscular tension and this gives it its relative longevity. I prefer collagen (Cosmoderm) for acne scars, but Resylane is also a good choice. I actually enjoy doing these injections since they are safe and provide lots of patient gratification.
Limitation: Deep ice pick scars do not do well. You did not ask about other treatments for acne scarring but some very good ones are out there, including chemical peels, dermabrasion, laser resurfacing and Fraxel. They all do well. The gold standard would be laser ablative surgery, in which the whole epidermis is destroyed by light and then permitted to grow back in.
There can be problems with pigment differentiation and scarring. Fraxel is a fractionated laser that removes small areas in a rapid and consistent pattern. The results are not as good, but there is less down time, and this is a far safer technique.
Also, there are various suture techniques. These include punch grafts, in which the acne scar is punched out and then the skin is gently sewn together, and subcision, in which the strands tethering the scars to the skin are eliminated and fillers injected. Plain skilled surgery is another means of correcting the problem.
Hope this answers some of your questions.
