My machine defaults to a 2. something. It seems to be just peachy for normal piecing. If I am paper piecing I drop it down to a 2.0 or less. If machine quilting (rarely) and/or attaching binding, I will up it to 2.6 or better. Generally speaking - more layers - longer stitch length. Paper piecing, you can stay with the default but it makes it more difficult to rip out the paper and, during that process, has a tendency to loosen the stitches, hence the shorter stitch length for that technique.

I use a 2.5 for piecing and a 3 for quilting. My machine defaults at 2.5 and I haven't had any trouble with my patches coming loose.
I'm pretty much a newbie too. You will find lots of help on this site.

My machine defaults to 2.5, but I lower it to 2.0 for regular piecing, and 1.8 or 1.6 for paper piecing (which I can do, but don't really enjoy).

For basting, or for stitching "test" items, I bump it all the way up to 5, which is the maximum. Makes it easy to rip out afterwards. :)

thanks for all the good info!!

The same for me, I found my piecing looked better and was more secure when I switched from 2.5 to 2.0. Something I heard from a couple of very experienced quilters on the Quilt Show website.

Isn't that strange? My Babylocks default is 2.5 They must change the default in the same brands or newer machines, I think. Interesting topic.

I use 3 when piecing. I always backstitch at the beginning and end of a stitch. I've never had a problem with the stitches being loose. I think it depends on how balanced your stitches are and the perfect tension to get balanced stitches. Not many know what a balanced stitch looks like. Machines are set to sew poly thread with poly bobbins. That is the auto/normal tension the machine is set for, even the bobbin tension. You have to change tension with every type of thread.

I do what Nammie does.

I have older machines that don't default to anything - they are where I put them. No decimal points either, just a dial or lever with numbers on it. For piecing the dial or lever is somewhere between 2 and 3 but closer to 2. For machine quilting where I'm using a walking foot I like the dial to be somewhere around 3. Is there anyone else out there that uses older machines that don't have all the automatic gizmos?

While we're on this subject... what about Batiks? I am just starting a Gimme Diamonds quilt in batik with inner sashing. My Janome defaults to 2.2, should I be using a longer stitch?