Hmmm, tricky. MA Marignon's national summons are all Fire/Astral, with the crown jewel being the Heavenly Choir (144 Astral gems, S7F2). Their best native summoner is the Grand Master (2TR, cap-only), which has a guaranteed F3S2, a 100% shot at FAES, and another 10% chance at another FAES. F3S3 is a safe bet, and F3S4 is possible, but not likely. However, even with with F3S2 alone, you can try to catapult up with magic path boosters - Starshine Skullcap gives +1, and you can try to trade for Crystal Coins (or empower/pretender into combined Earth/Astral paths) for another +1. If you can hit Construction 8 first, you should be able to grab the Dimensional Rod by using any S3 caster for a dangerous-but-useful boost (+1S,
Horror Marked, Unremovable, Quickness,
Increases insanity every turn), and if you can grab a F4S2 Grand Master on the side, in addition to having him forge Flame Helmets (+1F), slapping just +2S in boosters on him lets you create that marvel of marvels, The Forbidden Light (+2F, +2S,
Horror Marked, Unremovable). An outside chance also exists if you can get lucky with a A2F3S2 Grand Master, who can then forge the unique Tome of High Power (+1A, +1S,
Horror Marked). With +5S in boosters available to you, you can then churn out Rings of Sorcery and Wizardry, and call down Heavenly Choirs like the Pearly Gates are going out of business, as long as you can afford those exorbitant gem costs. Of course, you have to either win the race to Construction 8 (for Dimensional Rod), obtain a Crystal Coin somehow, or get really lucky with those 10% paths on your Grand Masters.
When considering the pretender, it's useful to know that Marignon is extremely resource-heavy. Their main-line forces are around 20-23 RES each, and their cavalry arm exceeds 50. Actually, generally speaking, Marignon has some rather difficult and contradictory needs - it needs high Dominion for its sacreds, high scales for its main-line forces, and high paths for any blesses, which combine to make Dormant almost mandatory at a minimum. Its main-line forces are decent but not exceptional, and its cavalry arm is too expensive to mass in the early game. Its sacred flagellants are both cheap and eminently spammable, but have all the durability of wet tissue paper, and are worthless unless you have a great bless, at which point they hit mediocre. For scales, Production 2-3 is almost mandatory to deal with the resource costs. Growth helps counteract the weakness of old mages, but Order gives more gold for your early expansion and is thematically appropriate for the zeal of the people everyone never expects.
For paths, you can reduce the gambles on Grand Masters by putting Air, Astral, and Earth on your pretender. A2E2S2 is the bare minimum in this respect, but higher is obviously better, not the least because 4 unlocks those blesses for your angels. A3 gives you Arrow Fend, and A4 gives you the Precision bless and Mass Flight. S4 gives you an MR bless, not to mention Mind Hunt and Gateway. E4S3 gives you the Sword of Many Colors (+1 FAWE) and E4 gives you a Rejuvenation bless (critical, since fatigue's always a killer). Alternatives are Earth/Astral (useful bless, guaranteed Crystal Coins) or Nature/Earth (minimum N4 for Gift of Reason to convert angel soldiers into additional commanders for further thuggery, preferably N9 for Regeneration and E9 for Rejuvenation). For a chassis, the Great Enchantress is an option for additional Astral gem income, but she's more expensive because she needs to be built up rather than starting with high Dominion and/or paths. Statue of Order is a cheap but immobile option for E9S9 builds, while the Titan of War and Wisdom is an option for AES builds and the Statue of Fertility gives the perfect baseline for N9E9. Earth pretenders also have one more bonus - you're going to be spending gems like water on these boosters, so hitting E3 for that Dwarven Hammer will save you quite a bit.