The aircraft are very similar in terms of onboard equipment; they both will share the same growth powerplants, the CF34-8 and the Epic Primus avionics suite. The roomier capacity of the Do728 is superior and passengers are demanding it now in regional aircraft. If you say you work for CrossAir, here is where you will see the major differences.
Dornier is located in Germany and the production facility is in Oberphaffenhofen, outside of Munich. The Do728 is being produced there, in a much closer proximity to Switzerland, where CrossAir is located. Where is, the ERJ-170 is being produced in São Paulo, Brazil. If for any reason you ever need parts, which will happen, you would be in a better proximate to the production facility. These are new aircraft, some parts may not be available and this sometimes forces removing the parts from production for the customer. It would benefit you more to be with Dornier in that instance.
Now the biggest factor you will discover, Customer Support. Dornier offers our customers, 24/7 technical support something Embraer does not. You can call us at the Global Support Help Desk and get detailed technical assistance with the Do728. You will find that Embraer does not offer this. We both offer Field Support but they have no help desk. So when you have questions, which you will, you will have to call Embraer and wait, wait wait. They will get back with you on Monday; we are always there for you anytime 24/7.
Of course, I am biased, I work for Fairchild/Dornier as a Technical Representative in San Antonio but I love this airplane. Let me make an additional point about why your ERJ-170 is late. First, during the production process, Embraer decided to keep development costs low. Now at the end of the production, they have ran into problems with the Fly-by-wire (FBW) and software introgration. Reason, they didn't have a development platform like Dornier constructed. It's called an "Iron Bird", we have already put 1200 hours on all the flight controls and associated systems. This allowed us to work through 64 flaws and correct them ahead of time and at least 12 of these required redesign. So we fix our bugs ahead of time, you will get the ERJ-170 with many of these bugs and then you will be expected to fix them.
I hope that was helpful, feel free to ask more questions and ill try to help you.