Frankly, I don't use either. I mentioned in another thread that the issue with Rhinos (and inherently Razorbacks), is that any competent opponent is going to have enough anti-tank to reliably kill a Dominus class knight in a single round of shooting. Personally, I find that if you are looking for a heavy weapon platform, Devastators are a better option. They are much easier to get in cover and have a wider variety of weapon options.
Armour is inconsequential in this meta, I find. You have to build to be able to take on Knights, which can make lighter tanks irrelevant.
It really is a shame, because two of the most iconic vehicles in this game for Marines (Rhinos and Drop Pods) are practically useless.