There is no simple answer to this question. Different people use different programs and they are all different in price and functionality. There is no such thing as a good automatic digitizing program, you will have a big learning curve no matter which software you chose. You need to understand the construction of the a design and why it is put together in a particular way. I personally use Generations. I also have pe design next but I don't like it. Both of these are quite expensive programs up to $2000 australian each, there are cheaper ones on the market but I have never used them. Quite a few of the cuties use Embird, I have not tried it, but it seems to be popular.
I think there is a free one that you could get started on but I can't remember what it is.
Alice.

Alice has given you a brilliant answer -)
I have Ped design 7,and generations bit I prefer my Embird and love it - :-)
I believe its a matter of which one you get used to using
Big hugs from London
Maria xx

And there is a free one http://www.freesierrasoftware.com/stitch_era_universal.asp

I have it, but haven't even tried it yet.