I recommend the DeWit traditional gardening knife, which compares to a Hori-Hori knife. On the plus side, the garden knife is a multiple purpose tool in the garden for such jobs as digging and cutting while also serving you well for transplanting.

If I could afford to purchase both a garden knife and a DeWit transplanter tools for my toolshed, I would buy them both. However, I lean toward tools that do more than one job in the garden. I also factor in cost. The gardening knife cost about $45, whereas the transplant tool runs $25. On the face of it, the transplanting tool seems to be the likely choice based on price and effectiveness for transplanting, but, for my money, I would buy the gardening knife. Here's why: the knife blade is only about 3-inches shorter than the transplanting tool, so, unless you have to transplant a whole bunch of deeply rooted plants, I think the knife will suffice for almost any transplant job in your garden. Plus, the knife can be used for other gardening tasks such as weeding, cutting roots, removing plants, sod cutting, and splitting perennials. And I need to do all of those things in my landscape. I certainly don't want to buy more tools for those specific tasks. The cost of which would quickly exceed the $20 or so dollars I save by buying the transplanting tool. Plus, in a pinch, the traditional gardening knife can serve as a small hand axe. However, if you are going to be transplanting deep-root plants or are working in a rock garden, I would go ahead and buy the transplanter, if you already have a Hori-Hori knife in the shed.

Here is a link that might be useful: Which Tool Makes Transplanting Easier for You