Funny you should ask...I just got out this 10-year-old project yesterday. It a flimsy I never quilted because I wasn't sure it was done. Anyway, I had a vision of cats on the quilt somewhere so added the two after piecing. If you can see clearly there is no puckering and the appliques seem to have had no real effect on the quilt itself. My machine (Brother Innovis 1250D) has applique stitches built in but I think the satin stitch set at the longest/widest setting would work. Good luck.

Consider raw edge applique where you FMQ around the designs with a straight stitch 3-4 times-- I like to use a slightly darker thread - it adds a little depth- here's one of my duckies on Pinterest:

https://pin.it/dtNHDIu

I agree with those who said zigzag or buttonhole/blanket or raw edge. My biggest concern with satin stitch is that the number of perforations close together tend to weaken the fabric. They look good on things that won't have to be washed frequently, but are a stress point for something that will get a lot of wear and tear, such as a baby quilt.