Transfer in PHL is not bad, all of the terminals are connected by walkways and immigration has a decent capacity. Two hours should give you a very good probability of making your connection.
I am not fan of US, but the times I flew with them they brought me where I had to be. Business may be less luxury than other airlines, but you pay less too.
it evens out.
If you have someone else paying, I would go for LH... If cost is an issue for you, consider US.