I like the top one best. No reason, just do! Will wait to see the quilt when you're done!

A challenging pattern for sure, and my preferred arrangement would be determined by how I intended to quilt it.

When you say picnic blanket, are you envisioning a heavier material than standard quilting cotton? I'd have concerns about the narrow triangle points and bulk if I were considering a heavier weight.

re. the triangle in a rectangle construction aspect of your question -- what method(s) have you used thus far, and what approaches do yo like?

I was recently in a swap where one participant asked us to make paper pieced rectangle/triangles, which was not my favorite approach. I like using a tri-rec ruler-- I consider it a good investment for getting precise piecing. There are a couple of tutorials online that suggest using a printed guide, but most in the group had significant issues getting accurate final blocks.

So - my suggestion, as you have quite a variety of blocks in your design -- make one trial block and see how it goes and where you run into issues, then problem solve from there.

I like the one with the big diamond in the middle.

It's a picnic blanket because, knowing my brother, he'd otherwise stuff it into a closet as "heirloom" and I prefer my quilts to be used after I put that much work into them. I don't object to worn out quilts, I'd rather make them another. I am using cotton for the front and heaver cotton for the backing.
I've not done HRT's before but I have Tri-recs so I'll give that a go. I've done a few mock-ups and like the method of HRT's that makes two at once but I have to over cut pieces and then square them up and I really dislike squaring up. Beggars can't be choosers, I suppose.

Love the first layout!!! And like your reasoning on calling it a picnic quilt too. I definitely agree that quilts are made to be used.

I prefer the 2nd one also. I too think it is easier on the eyes. I reminds me f the pineapple block. What colors are you going to use? Be sure to share the finished quilt.

I love the first one.

Go with the first one. It's beautiful!

I like number one because it is more interesting visually. Of course much will depend on the final choice of fabric and the likes of the ones receiving the quilt. The more avant-garde would like #1 but the more traditional may like the second one better. Both are fine as presented and would be a good exercise in quilting and creating an illusion. :):)