First of all, the material taught during your first two years of medical school, the pre-clinical years, is pretty consistant across all US medical schools and cover generally the same basic science subjects. There are indeed variances in how the material is presented/taught, differences in focus, and in the time allotted to each basic science, or subject. In general, these differences are related to individual school preference, their mission, and adopted curriculum style, such as traditional-based, systems-based, case-based/PBL, or some hybrid, etc. Beyond these school-based variances, the major difference between the pre-clinical curriculum at an osteopathic medical school (OMS) and an allopathic (AMS) one is that at an OMS, you are required to learn OMM, which generally includes related lab and lecture material. Otherwise, you won't be able to tell the difference between the two. While it hasn't ever been officially expressed to me (nor have I seen any data, comparative or otherwise), from what I have gathered, there may be some fewer hours spent on some basic science subjects here and there, but I doubt that this is exclusive to the osteopathic program(s) I am familiar with. I'll leave you to make any reasonable connections you want about that, perhaps relative to the inclusion of OMM.
I think it's also fair to state that OMS' are going to bias their curricula and related elements toward the COMLEX, while AMS' are going to bias theirs toward the USMLE. As a result of that and speaking rather generally there may be differential trends in emphasis across each group, along with the inclusion of OMM in the OMS' curricula and variations due to individual school preference. Yet, overall, I'd say that the curricula across all US medical schools, osteopathic and allopathic, are significantly more similar than different. Indeed, you would be challenged to observe any differences, other than the obvious inclusion of OMM. If we were to divide the two groups out by commonalities among each group and differences between the two, you'd likely see that the differences between the two are not significant enough to demonstrate a general professional impact. That is to say, both work side by side during rotations, residencies (many osteopathic medical students opt to do allopathic residencies), fellowships, and as attending physicians without much, if any, observable difference relative to their designation. Basically, the two are professionally-equivalent and practice to the same standard of care, which in itself expresses the equivalency of their training. Also, each year, many osteopathic medical students prepare for and take the USMLE, in addition to the COMLEX, and some even out-perform their allopathic counterparts.
The point is that you'll get a solid pre-clinical education anywhere you go for medical school in the US. Perhaps more than ever, medical school is medical school, whether it is an OMS or AMS. Anywhere you go, you'll have adequate preparation. It's up to you to choose an individual variant that appeals to your goals and personal style. I hope this helps.
