Totally different types of machines. The B3030 is an ultralight ladder frame design. The CK30 is a heavyweight traditional style. Both are loaded with deluxe features but both are suited for different tasks. If you are maintaining a lawn, the B3030 with a mid mount mower would be an excellent choice, its light weight also makes it a great machine for tilling the garden. Its loader is adequate for work around the house. The CK30 is much stronger with higher capacities in every way, it would be the better choice for heavier tasks like box blading, pulling logs and heavy loader tasks.
</font><font color="blue" class="small">( If you are maintaining a lawn, the B3030 with a mid mount mower would be an excellent choice, its light weight also makes it a great machine for tilling the garden. )</font>
Bob's pretty much right on with his assessment, however, I don't think the weight makes a whole lot of difference for tilling if you have a tiller that covers your tracks. After all, there'll be no rutting! If it's too wet, either of these tractors will be too heavy, and you won't be tilling in mud for good results anyway.
If mainly for mid mount mower (MMM) cutting, the Kubota's mower is better. John