Quick question re: booking a codeshare flight through UA or LH

Hello,

I am ready to book two business class tickets for my wife and I to travel to Abu Dhabi in early December. Since this is a codeshare, I'm wondering what my best approach is in terms of:

a) sitting with my wife (being able to select our seats)
b) PQMs (@ 150% in business)
c) operational issues (and being put on the next flight in the same class of service)


The cost of the tickets is identical...

The schedule:
Flight 1- ORD to FRA (744) on LH
Flight 2- FRA to AUH (330) on LH
Flight 3- AUH to FRA (340) on LH
Flight 4- FRA to ORD (777) on UA

Please let me know if you see any disadvantage with booking through UA (I have silver status here and this trip will certainly help get me closer to gold.

Thanks for any advice you can offer,
Fred