IMO, you can't beat Spot Shot. But I have friends who love Resolve carpet cleaner. The rug cleaner I hired recommended using regular dishwashing soap for carpet stains.

I've posted this recipe before. it really works great on any carpet, even old stains. Mix one bottle of hydrogen peroxide (about 99 cents), half again as much plain water (need not use hot H20), and a good squirt of Dawn dishwashing liquid. Stir and pour on stains, rub with a clean washcloth and blot as much of it as you can. This mixture cannot be stored, so discard the excess or make a smaller batch.