I had 2 Yanmar B50's. It is a 10,000 lb machine, and you won't be happy with anything smaller. I compared it to all others including brand new models. Nothing even came close. More power and faster cycle times.
Used them for many years in an excavating business with minimal problems. This was in the late 80's through mid 2000's. Parts are alot easier to get now.
Do not get anything with a "knuckle boom" where the dipperstick swivels separate from the boom. On most the boom will swing independent of the machine which is nice for digging along buildings.