First of all, let me congratulate you on being the recipient of not one, but two quilts - yippee!! The 1000 pyramids quilt is gorgeous and you're lucky to have it. Now, this is my own personal opinion, but either of your two methods would work, George Bonesteel says that she uses a small zig-zag stitch in lieu of SID, - I've started doing that and it does look nicer than my usual SID quilting. Also, your meandering quilting looks fine to me. One thing to consider is that probably about the time your grandmother made those two quilts, sewing machines were becoming very popular and were used more and more in quilting quilts. I've seen antique quilts with both hand and machine quilting, so either was OK back then. I don't think there is anything wrong in using machine quilting, either SID or meandering. Personal preference. I may have confused you even more, but whatever you decide, your grandmother wanted you to have these quilts and I'm sure she will be happy with whichever way you choose to complete them, as well as proud that you will finish the quilts she started and meant for you to have. Happy quilting.