Oh, haha, I was going to post a comment several times here, but whenever I got around to writing one, something distracted me.
Personally I like both of them and I think both have their own uses. The Taurox one is cheaper and it's a great addition to a Taurox-mounted core. That way you can play SWAT-style with a bunch of commandos embarked in armoured trucks. Kitted out either base with the battle cannon/autocannon, Taurox spam will give you enough S7 fire to pop regular transports such as Rhinos and Chimeras and them being Fast vehicles means that you will get plenty of occasions for some side armour goodness.
The valkyrie formation seems to be a bit cooler in that it uses one of best looking flyer models, gives you access to your only high
str weapon in the Codex(lascannon on a 12/12/10 flying frame) along with anti-air potential and has greater mobility, but it gets very pricy very fast. That being said dropping Scions from them even onto terrain is perfectly safe thanks to their Move Through Cover special rule with some twin-linking goodness there.
Overall I think they're definetely a must-have in every Militarum Tempestus army because at the fee of a single commissar(25pts) that is fairly useless you can get everything you would take normally, but with additional, fantastic rules. They also let you expand beyond the 6 troop limit in an army that depends in 90% on it's troop entries.
They could also be fine as addition to an Astra Militarum, Imperial Knights or any imperial army that lacks what they'd give it, as they're separate detachments that don't take up allied slots, which means that you can get some scoring goodness in fast vehicles that comes as a whole on a single reserves roll!