Twilight of the Armor is definitely the best. Are you willing to wage $20 on a game that's like 12 years old? I see Galciv2 Ultimate retailing at $20. If so, I think grabbing all the DLC and playing the campaigns makes sense. I found the Dread Lords campaign very fun; but you need to amp up the difficulty. Be prepared for a different, weird econony. Lots of strategy guides out there.
However, if this is just to bide your time while Galciv3 gets worked out, I don't think we can reliably plan on Galciv3 ever having all loose ends tied. I chose to forego being a Galciv3 founder and just now bought Galciv3+Crusade for precisely that same reason, and that hasn't quite worked out as I had planned.