The second one is rated slightly better in the reviews, but I'm not sure that either would be strong enough to handle several layers of nappy fabric etc. Its also handy to have a zig-zag stitch in addition to a straight stitch, so you can sew stretchier fabrics and go over the edges of fraying fabrics.
My sewing machine was around £150 (although they do come cheaper, i was lucky enough to get mine for Christmas!) and will last for years and is reliable enough to use for most sewing projects. Its come in handy many times when I've wanted to make curtains, tableclothes, napkins, cot sheets, pillowcases, aprons, shorten jeans, repair clothes and bedlinen, and make nappies, toys etc. Last week I recycled jeans and t-shirts into maternity jeans and bump bands! So I'm defintely getting my money's worth out of it and I'm not sure a cheaper, "mini" machine could have coped with all that!
Defintely worth saving up for one (or making heavy suggestions towards christmas time
), or seeing if you can get a good condition second hand one. Some shops have sales after Christmas when newer models come out. If none of those are options though, you can get some preloved mini sewing machines on ebay that dont cost too much, so you wont be wasting as much if it doesn't live up to your expectations!