I have the Asana, and have used the Blubber. The simplest way to describe the difference is that the Blubber is just more pad. It is thicker, stiffer, has no seams, is bulkier, and heavier. This means that when in use it provides more protection, but is also more weight/bulk to carry around and store. More is not inherently better. It is a tradeoff, and it depends what you are looking for.
I chose the Asana since I wanted something that was light and compact enough that it was a no-brainer to bring every time. It fits easily inside my main pad, even with other stuff wedged in too. It also fits easily in the car, no matter how full the car is for a road trip. I never have to leave it behind due to lack of space. And it pretty much always proves itself to be useful when out climbing. I don't find the seams to be a major issue in practice, though you do need to be aware of them when placing the pads (i.e. make sure the Asana seam is offset from the seams of the pads underneath).
The Blubber does provide better protection, and I initially planned to get the Blubber for this reason, but I realized that I would more often need to leave it behind on trips due to carry weight, car space, etc. I decided I'd rather have less pad that I can bring all the time, than more pad that I'd only bring some of the time.
Your circumstances may vary though. If you have a big truck, a big crew to carry all the pads, and/or your bouldering areas are a short walk, then the burlier Blubber may be the better choice. But since I have a smaller car, often am carrying all the pads myself to boulder solo, and sometimes need to walk a ways, I chose the more portable option. The Asana made sense for me, but the Blubber may make more sense for you. Either way though, these types of pads are amazingly versatile and a great addition to the kit.
The Send pad looks nice. More similar to the Asana in thickness, foldability, and general niche. I chose the Asana over the Send since I found a good deal on it with free shipping, so it ended up being (by far) the cheapest option at the time. Shipping on the Send pads is pretty pricey. But if price was equal (or not a concern) there may be a case for the Send over the Asana. Or if you are able to buy the Send while in Hueco and skip the shipping issue.