Welcome to Heresy!
Is this allied force purely for rules or do you have to like the models and want to play them? SW have some bad-ass rules currently with Wulfen and Thundercav, but I (somewhat obviously from my pic) prefer the aesthetic of BA. Plus BA got a nice boost with the Angel's Blade book: Assault Terminators and Sanguinary Guard can both make disordered charges out of DS and they can plug-and-play double-tapping Dreadnoughts now which is nice. Also there's a somewhat a point-cumbersome 1st Company meta-Detachment but can roll for DS from T1.
Outside of Drop Pods, the Golden Host Formation is pretty sweet. It's 2-5 Sanguinary Guard squads and either Dante or the Sanguinor. You get to choose whether or not to arrive from Deep Strike without rolling any dice, so no worries about Reserve manipulation, and you get a disordered charge upon arrival. It's not totally crushing but it's nowhere near weak. I've had a lot of fun with it and I use it at a minimal cost.
5x Sanguinary Guard - 3x swords, axe, power fist, two inferno pistols
5x Sanguinary Guard - 3x swords, axe, power fist, chapter banner