You didn't mention the H-1B lottery, but you should think about it before making your decision. If possible, it would be preferable to know whether your current H-1B application is receipted, although that information may not be available until May or June. Based on current numbers, each cap-subject H-1B application submitted in the first week of April has about 30% chance of being receipted in the lottery. If it's not receipted, you can try again the next year, but it's also possible that you could run out of OPT time (or STEM OPT time if you're eligible) without getting H-1B.
Another reason it may be unwise to abandon the job offer you accepted is because you already accepted their job offer and had them file an H-1B petition for you.
If after considering these factors, you still decide to change to the new employer, you can indeed do so by using OPT. If you get approved OPT, it is valid for any employer, as long as your employment is full time and is related to your major.
EDIT: The point about the lottery is that it's possible to get unlucky several years in a row and never actually get H-1B. Since the H-1B was filed for consular processing, it shouldn't cause any problem for your F-1 OPT regardless of whether it's withdrawn or approved. Even if it is approved, you don't have to proceed to getting the H-1B visa; you can continue your F-1 OPT instead. (In contrast, if the H-1B had been filed for change of status, and it got approved, that would immediately end your F-1 status and change you to H-1B status.) (There have also been some cases of H-1B applications messing up the F-1 SEVIS record due not to any law but to a DHS system error. If this happens, your international student advisor would have to submit a request to get it fixed. The worse case scenario is that in the meantime your OPT is adjudicated and denied, although this is uncommon.)