I haven't researched much yet...I just survived first year of medical school and want to take everything step by step so I'll focus on second year classes and then boards...
The biggest mistake that I made in my medical school career was not studying for the COMLEX as much as possible when possible. There is so much minutia and BS that your profs test that WILL NOT EVER make it to the COMLEX (or USMLE for that matter) and you will never see again.
My advice,
Youel's prep course. Just google it. I took his home based study course, well, over 10 years ago, I received a bunch of books and VCR tapes in the mail. THEY WERE WORTH EVERY SINGLE PENNY!! If this stuff even still exists, I am sure that by now it is more modern .e.g. discs, ipad accessible,etc.
Now, Yoeul's is geared for the USMLE. Back in my day, if you called customer service, you GOT CONNECTED TO DR. YOUEL personally! I asked him if he thought it would help with COMLEX. He told me that many osteopathic students call him up and thanked him for his help. I would agree, it was one of the best preps minus the OMM stuff.
I highly suggest that you get Dr. Youels stuff and review it every week. I wish somebody had told me this back in my day!!!
Also, there are the Northwestern Board review courses. These are geared specificially for the COMLEX and and they will reimburse your board fee if you fail.
Listen, I remember how medical school was. I know that there are gunners out there that are probably already signed up for the USMLE and have been studying for it back when they were in pre-med because if they got a score of less than 99% in anything, then they might not match into ortho, ent, derm etc.
As much as I hate to say this, you could be the brightest individial on the face of the planet, you might even find a cure for HIV for all I care, if you screw up your boards, it WILL ALWAYS BE HELD AGAINST YOU, no matter what you do, EVER!!!
Nobody wants to believe this but I've seen it more times than I care to mention. I'll give only one example. I recall once in my residency we were reviewing applicants. We had one spot left and it came down to two applicants. One guy had an awesome record!! Great grades, high USMLE scores, etc. He failed to match into ENT but argued on his application that he liked head/neck neuro, neurotology and was once a nurse on a neuro ward. The other applicant was mediocre and did not match into PM&R. I casted my vote for the later applicant, with the argument that there was more cross over in neuro with PM&R than ENT. I watched everybody else vote for the former applicant for no reason other than he had higher board score. Well, he lasted one year before he resigned. The other person went to a different program and today is a neurologist.
Okay, back to the point, no matter what you do, whether you take COMLEX or both COMLEX/USMLE, start your studies early!!
Also, DO bias, in my experience didn't have much to do with grades/scores as it did geography. DO's are a dime a dozen in Michigan and most of the Mid-atlantic. Out West, seriously, some PDs are not even aware that DOs can practice medicine and think they are the equivalent to chiropractor. I would base your decision to take the USMLE upon where in the country you wish to be located. If you want to practive in the mid-west or mid-atlantic, then you might be wasting your time.