I think it depends on the type of quilts you make. I know that I've always used a lot of 2 1/2" and 4 1/2" HST's but just lately I have been using 3 1/2" HST's. I usually make 12 1/2" blocks so these sizes of HST's work well for me. If I favoured 10 1/2" blocks, only the 2 1/2" HST's would work. Before you decide, think about your quilting style and what size will likely be the most useful.