When joining the blocks to make a crochet afghan, which method is better? Is there a notable difference between crocheting them together or sewing them together using a large eye needle and yarn? Is one method stronger than the other? Thanks.
If you crochet them together, even with a slip stitch, it will be ridged on one side. It is however, the strongest way to keep them joined.
And yet, should you ever had to replace a square (ink stain, koolaide, tear, etc), the sewing is much easier to redo and it all lays down flat. If your squares are varigated but with a different color scheme (blue and brown or red and pink) for example, using a color that will blend in with both is best. In other words, don't have a variety of colors and then use white or black to sew them together. It will look lazy and awful. A lot of folk like to border their squares in a solid color, then use that same color to sew them together with.
There are ways to join as you go, and I am including the google search that gives you tutorials that will help.