I'd go with the burst lightning. Gatekeeper is nice, but ultimately it's just non-targeted removal for BBB. The commitment here is a little scary, especially after my last encounter with black commitment on the first pick. The burst lightning is a great card in any draft, with minimal commitment and very good value-for-mana. You will practically never see a burst lightning on the second (or let's say third) pick, but you might come across a Gatekeeper.

[[Burst Lightning]]

I'd take the fetch land in all but the most serious of tournaments, like ptq or nationals etc. In those I would also take the burst, I could be cut on red but But burst is also splashable and gatekeeper isn't.