I would do the heads.
It will be more expensive up front. But you only have to do it once.
The most common cause of valve stem seal failure is excessive lateral movement of the valve, from worn guides. (worn guides cause seal failure, not the other way around)
There is no way to determine the condition of the valve guides without removing the cylinder heads. But I would assume they are.

If you do just the seals, how many times are you going to kick yourself for having wasted that money? If the seals go again in short order.

On the question of seal choice, in my opinion they are all created fairly equal. No reason to stick with BMW, when you can get the same or better seals for less $

Out of curiosity, what was the quote for the 2 repair options?