From optimization perspective: You should definitely take Pious Templar to get Mettle (Evasion for Fortitude saves) -- as it doesn't progress spellcasting, you should take it on your Ranger path. Take either one level (for Mettle) or three (for free Weapon Specialization). Take a couple of Ordained Champion levels for an awesome Smite which uses your Rebuke attempts. I'd suggest taking Holy Warrior feat since it gives you +1 to hit and damage/spell level of the highest War domain spell you can cast -- so with your War spontaneity as long as you had one high level slot available, you'd be getting +5 or +6 to hit and damage. At all times.
Actually, if you do go with Ordained Champion, be sure to be a Cloistered Cleric -- extra skill points and an additional domain whose power you can sacrifice to get a free feat (!!!). You lose nothing in this case as your BAB is governed by your ranger side anyway!
You might also want to look at Prestige Paladin -- and take Paladin of Slaughter (CE) variant. That'd give you access to paladin spells, auras and maybe even a mount. Be sure to take the Battle Blessing feat -- it'll let you cast all the spells on the paladin list as swift actions -- which is something you really want and need considering you're a melee warrior so anything that lets you full-attack AND cast in the same round is gold.
If you really want to emulate Gruumsh, you could take Eye of Gruumsh -- it doesn't progress spellcasting, so take it on your ranger side of the gestalt. I'd stop at level 5 though as it's when it gets Blindsight.
I'd go with Ranger/Eye of Gruumsh/Pious Templar // Cleric/Prestige Paladin of Slaughter/Ordained Champion on the other side. Pious Templar, Eye of Gruumsh and Ordained Champion work well together in that they all require you to take Weapon Focus -- which you'll get for free by being a Cleric with War domain.
(Be weary NOT to lose more than 1 cleric spellcasting level though as that'd put you a whole spell level down and in 99% higher level spells access trumps pretty much anything else. I mean, there are some cases where it's not true, but as I said, 99%.)
You could even take Bone Knight if you're fine with being somehow connected to necromantic forces -- it's one of the most powerful cleric PrCs in that it gives you a BUNCHLOAD of immunities as you level up.
You could also take one level of Lion Totem Barbarian on the ranger side to get Pounce -- being able to use all your melee full attacks on charge is probably the best ability ever for a melee warrior.
So, keeping all that in mind if I were you, I'd go with: Lion Totem Barbarian 1/Ranger X/Pious Templar 1 (or 3)/Eye of Gruumsh X // Cleric 4/Ordained Champion 3 (to not lose the second spellcaster level; or 5 if you're fine with losing those 6th level spells, but the 5th level abilities are meh! 4th is quite OK)/Prestige Paladin of Slaughter 1 (again, same; or 2 if you are fine with losing those 6th levels spells...)/something else X/Contemplative 1 (one extra domain in exchange for... nothing? yes, please)