They're all nice, and appeal to different wants and/or needs. It can't be easy for a small team to maintain multiple flavors, although the choices will ultimately attract more users and patreons, helping the project growth.
Like the approach that Antergos does relative to their live DE installs. One image, choice of any DE.
I may dabble in the various spins, but always end up selecting the flagship of the project. For Solus, that is Budgie. It's where a majority of the development and resources are consumed. In my experience, including Solus, it's the spin that always performs the best. Mint & Cinnamon is another example. Many do Cinnamon, few do it better than Mint.
Recently, I installed Solus Mate and gave it a test run. It's nice, but my experience says it needs some bug attention from a DE-specific dev.
So, back to the flagship. Works great!