Depending on the shades, side by side alternating shades can look streaky, in my experience! But it depends on the clients hair, if it's highlighted a lot, I just match each strand, not following a particular order, this gives the most natural look.
I had a client who was a #2 for 3/4 of her head and a #4 on the top layer, so I just did rows of #2 for most of her was then the last few rows I did in the #4. Was a perfect mix.
But yeh, depends entirely how the tones are mixed in the clients own hair x