Sorry for the confusion. I kind of posted as I was doing my research and over time what I've learned has kind of changed. Yes Acetyl-L-carnitine does appear to be the best one to take. The other one "propionyl-L-carnitine" or (glycine propionyl-L-carnitine) (aka GPCL or PLCAR) may also be beneficial. I've flip flopped back and forth as to which is better but I read conflicting things. Acetyl-L-carnitine will help with brain and nervous system, which may be where the important androgen receptors are. propionyl-L-carnitine may help in other parts of the body better. So the short answer is Acetyl-L-carnitine. If you can, get both and take both which is what I do because I can't decide and happen to have bought both. I figure it can't hurt to take both. These are the two most "bioavailable" versions of l-carnitine. Just plain l-carnitine is not as readily bio-available and not as beneficial to take, though I can't say there isn't a benefit to taking it, it doesn't seem necessary if you're taking either or both of the other two. Clear as mud?