Hey m8. If you want to grow critical mass get it from the original breeder which is Mr. Nice. CM is a heavy yielder and a tough plant. It does well topped. Excellent cash cropper and it's quality stuff too.
If you're looking for a widow crossed with something for increased yield I would go with Fruity Chronic Juice by Delicious Seeds. Every single Widow cross I have smoked, with the exception of Fruity Chronic Juice, has been garbage. There are a few different FCJ pheno's. All have generally the same flavor which is really special. They have the spicy of the widow and the sour of the chronic. Totally frosted over. Very good yield. The smell is good too... a mixture of pine and tropical fruit.
Widow x big bud is basically what Fruity Chronic is... Chronic is a big bud cross.. and widow is widow. Widow is my favorite...but it has to be the original.. there are a dozen other breeders that sell white widow seeds but all are garbage. So i'm particular when it comes to widow and it's crosses. Fruity Chronic Juice is the original Widow mixed with a nice chronic plant. It's very good m8.
If I were picking one based purely on yield i'd go with critical. If you want a good mixture of flavor, yield, potency i'd go with FCJ..which beats out CM in most categories.