Edelweiss is a holiday airline versus Austrian which is a full service / network carrier.
The seats are virtually the same, very little difference there- screens may be larger on Austrian.
Other than that, service will be similar- Edelweiss has a very nice onboard experience & so does Austrian.
If the departure point doesn't really change much for you, I would suggest taking the option with Austrian, the ground experience in Wien will be a bit better than in Zürich & the 777 has a wider cabin and larger overhead bins (you mentioned travelling with an infant....)
Have a pleasant journey
