Other than the powers they are trained in, is one BO better than another?

Yes, all BO's are not created equal. There are, in fact, three key differences between various BO's.

Space Traits. Some select few BO's come with traits (not skills but traits) that help in space combat.

Specifically, the Liberated Borg from the preorder and in very rare cases certain Saurian officers can have the efficient trait. This trait becomes useful once you start getting some of the later efficiency skills (Similar to how Warp Core Theorist becomes useful after Warp Core Training). Efficient Saurian officers used to be quite common, but I haven't seen one in a while (aside from the one manning my science station). They may have removed the trait from new officers to preserve the uniqueness of borg Bo's. I have also heard of BO's with something called "Proficient" but cannot confirm this, since I do not have one in my possession.

Superior Ground Traits

Superior ground traits (e.g. Superior Luck, Superior Peak Health, Superior Mind Meld, etc.) are available on Blue and Purple Rarity officers. These abillities are better (or sometimes new and unique like superior mind meld, only saw this on a Purple rarity Vulcan on the exchange) than what your stock officers have and can be quite useful if used properly, e.g. with 4 officers with superior luck, you will notice a lot of exposes and crits which can be leveraged effectively.

Higher Tier Skills

Common BO's usually only come with level I and II skils, Blue and Purple rarity officers can come with level III skills, but these can be trained to your other BO's.