The pill is way more effective than the withdrawal "method".
From Wiki:
"Like many methods of birth control, reliable effectiveness is achieved only by correct and consistent use. Observed failure rates of withdrawal vary depending on the population being studied: studies have found actual failure rates of 15-28% per year.[2] In comparison the pill has an actual use failure rate of 8%, while the diaphragm has an actual use failure rate of 16%.[3] The condom has an actual use failure rate of 10-18%.[4]
For couples that use withdrawal correctly at every act of intercourse, the failure rate is 4% per year. In comparison the pill has a perfect-use failure rate of 0.3%, while the diaphragm has a perfect use failure rate of 6%.[3] The condom has a perfect-use failure rate of 2%.[3]
The primary cause of failure of the withdrawal method is the lack of self-control of those using it. Poor timing of the withdrawal can result in semen on the vulva, which can easily migrate into the female reproductive tract. Some medical professionals view withdrawal as an ineffective method of birth control.[5] In contrast, a recent study in Iran found that provinces with higher rates of withdrawal use do not have higher fertility rates, and that the contribution of withdrawal use to unintended pregnancies is not markedly different from that of other commonly used methods such as the pill or condom.[6]
It has been suggested that the pre-ejaculate ("Cowper's fluid"), fluid emitted by the penis prior to ejaculation, contains spermatozoa (sperm cells), and is easily drawn into the vagina by capillary action. However, several small studies[7][8] have failed to find any viable sperm in the fluid. While no large conclusive studies have been done, it is now believed the primary cause of method (correct-use) failure is the pre-ejaculate fluid picking up sperm from a previous ejaculation.[9] For this reason, it is recommended that users of withdrawal have the male partner urinate between ejaculations, to clear the urethra of sperm, and wash any ejaculate from objects that might come near the woman's vulva (e.g. hands and his penis).[10]"