I agree with Doelake. When I purchased my 2003
B21 it came with a 16" bucket and I assumed that was the largest available. After about 200 hours I found out there was a 24" bucket and what a huge boost in productivity that was. The increase in volume is much more than just the increased width - your heaped capacity goes way up. If you are only doing trenchs, the 18" may be fine but if like me you dig around foundations and sometimes dig out larger areas, the 24" will be money well spent in the time you will save. It is definitely much easier to deal with rocks with a larger bucket as pointed out.
After purchasing the 24" bucket I don't think I ever used the 16" again because I had a 10" with the
B21 for shallow, narrow trenching. As others have stated and I can confirm in clay soil it can take some shaking to empty a narrow bucket. However a narrow bucket is very handy when trying to dig around tree roots in order to remove a stump.
I traded the
B21 at 1,800 hours for a slightly used (180 hours)
B26 and had to take it with the Quick Attach 18" bucket. I knew I would need the narrowest bucket and so purchased the 12" QA but baulked at spending ~1,300 for another 24" bucket. That was when I discovered that you can by the QA plates from Kubota for about $165. I purchased a set, cut the
B21 ears off the 24" bucket and welded the QA plates on and had a 24" bucket for my
B26. In two years I have not used the 18" bucket - the 24" and 12" provide the flexibility I require.
This year I plan to add a 24" or 30" ditching (no teeth) bucket to my collection. Is anyone interested in a slightly used 18" QA bucket for a
B26?