All four of these games are premised on constructing some kind of thing on a grid.
Reef and Tiny Towns construct on a 4×4 grid while Azul and Sagrada construct on a 5×5 grid.
Tiny Towns and Reef start with completely open grids and allow for pretty much completely open placement, though those decisions then create constraints on future opportunities.
Azul and Sagrada both begin with templates of sorts (though Azul has a more open possibility), which creates external constraints, both because of their patterns and because of external constraints like placement rules (can only place orthogonally adjacent, etc.)
I set out on this experiment to see if we “needed” to keep all 4, or whether they overlapped to such an extent that perhaps one or more might be dispatched from our collection. But they all play sufficiently differently that I feel like they are very different games that I might want to play under different conditions. Azul is more relaxing than Reef or Tiny Towns, which in some ways feel more stressful because of the internal constraints that you impose on yourself. I love the pattern-matching in Sagrada and Azul, and the essentially puzzle creation in Tiny Towns and the vertical component of Reef.
In short, if you’re into game collecting with the purported intention of playing, much like the pandemic has made us (ok, I’m making M complicit in this — this is essentially my rodeo that he willingly shows up to play in (M here: this is absolutely the case as I, of course, have zero books, comic books, or records that I have not read or listed to)), I think having all 4 in a collection is well-justified.
Here are our overall ratings of the 4:
Petra: Sagrada > Azul = Reef > Tiny Towns
M: Reef > Tiny Towns > Azul > Sagrada