Which is the best street in Yarraville?

This is a tough question as you have not specified what you are really looking for in a street in terms of locality, public transport etc....

Streets around Cruickshank park are very nice! they can be on the expensive side though so keep a watch out! others streets such as Powell Street are lovely and leafy with great proximity to train stations!
Also try Tongue or Drew street, both have come with great recommendations form friends!

Hope this helps :)