As Hive account@jringo points out none of these "competors" have any products or platforms live yet. They are pure speculations and token sales. They have a theory while Gridcoin has a real viable platform running.

Gridcoin is a free to use, based on voluntary work. We reward projects users on their behalf, no cost for "renters". All our "competitors" want the cost to be handled by the renters.

SPARC openly admits in our reddit forum that their whitepaper is outdated and invalid, right on the beginning of their token sale! That's insane.

I don't think anyone dislikes some competition, I mean we have another 500,000+ users on the BOINC platform that can join any day to compete.

Development is not slow but very much alive and there are going to be paid developers soon enough. The SPARC team has done a very poor job on collecting their facts.

Additionally:
I would never join a project that keeps track of their users by posts on a forum. They have a centralized way if collecting stats and distributes tokens.