My philosophy is the make the best decision I can based on the information I have available to me at the time. The raid team is planning to stay Alliance. We're currently 11/11 N and 3/11 H in Antorus.
All I know with certainty is I want to play a Zandalari Druid. Their travel forms are dinosaurs and some of the data mining hints ALL their forms might be dinosaurs.
My highest Horde toon is Kishuf, the mage I boosted in Warlords. I decided to level him rather than use the boost I got with the Battle for Azeroth preorder. Once I get him to 110, he can do the Nightborne and Highmountain recruitment. I'd love to see those stories. Then once Battle is out, he'll level to 120 and do whatever is required to unlock Zandalari.
I have no idea what I want to main for Battle on the Alliance side. Honor's Hammer, my Paladin, has been my main for every expansion except for Cataclysm where I started out with Theogrun, my Hunter. Even then, I switched back to Honor's Hammer about halfway through. He's a hard habit to break.
The other option I'm giving strong consideration to is going Druid on the Alliance as well as the Horde. I already have a max level Night Elf Druid alt, Tivonicus. I wouldn't have to learn another class as I bounced between my Alliance toon and my DinoDruid. Druid's have the most flexibility of any class in the game allowing me to waffle on my role choice for quite some time.
My other max level Alliance toon in my Dwarf Hunter, Theogrun. He's a great deal of fun to play, and an Engineer which is my favorite profession in the game. While its never been a strong money maker, it looks to be getting some fun items in Battle. Hunter provides the least amount of flexibility. If I get the tanking itch again, I'd have to start over with another toon.
I'd eventually like to level a Monk as an Allied Race but the only option on the Alliance side is the Void Elf . I know I'm weird but I'm really not all that enthused about the Void Elves.
I am excited about the Lightforged. I plan on making a Lightforged Priest once I get exalted with the Army of the Light. I have a max level toon of every armor type except for Cloth. I have heard Discipline is the least squishy cloth class you can level. He'd pretty much always be a transmog farming alt as I've never liked the fantasy of Shadow. It's not something that appeals to me.