When you are starting to sew and don't know if you are really going to like it, I would recommend cheap sewing machines that are affordable. If it is easy on your pocketbook, you can buy it and try making different projects to see if this is going to be for you.
You may just need a sewing machine to use for making repairs. Like a torn seam, the kid's ripped a hole in their shirt, or even hemming up a dress that is too long for you.
You can get a machine for your kids to learn on. You won't want them learning on your expensive machine, so getting them their own that is affordable for you is a great idea.
Different machines come with different stitches. The basic machines may only have a few stitches, which if all you are going to be doing is mending, a few is all you need.
Some machines come with hundreds of different stitches. The more advanced sewer uses lots of different stitches to vary their projects. When you can change to a different stitch, you can make something look completely different than one you did with another stitch.
Quilting, darning, embroidery all use different stitches and as you become more experienced, you can try out the different stitches to see what they do and how they make your project different and more exciting.
Some machines are called multi purpose machines. This machine is like a little work horse that you mainly will use as you are learning to sew and it is great to use for projects and crafts. It usually has some different stitches, forward and reverse, hand switch or pedal and other features.
A lightweight sewing machine is great when you are in a sewing group that meets at different houses and is easy to carry. Let's face it, you can't lug your big machine to a sewing class or group! These machines are easy to put up in a flash and take down just as fast. These lightweight machines are great for kids to use too, as they can get it out themselves and set it up, and put it away when they are done.
Heavy duty machines are strong work horses. These are for heavy projects, like quilt making when you have a lot of fabric you have to sew through -- like your top piece of fabric, then the lining to make it fluffy, and the bottom piece or back piece. A lightweight machine will not be able to go through all these pieces of fabric.
Sometimes your jeans might need a different length on them and you will not be able to sew that hem on anything but a heavy duty machine. Trust me I know from experience when my daughter-in-law tried to sew up her jeans on my little Singer -- which then had to go to the shop to get fixed!
As I said before, quilting needs a different type of machine in order to make them. My sister does a lot of quilting -- from hand ones to the ones on machines -- and when she is working on the machine ones, she gets out her work horse.
When you are finished sewing the quilt together, many quilters do top stitching all over their quilt to "finish" it off so to speak. This requires you to be able to move your fabric in all different positions, and you may vary the stitches too.
A little mini machine is a great machine for kids. It is also great for a quick repair job you might have that you can whip it out quickly and get it done fast. A little mini is also good to have if you are taking a class or go to a sewing group.
A lot of the portable sewing machines come with a carrying case, and you will want to get one especially if you are using your machine for groups or classes. A carrying case is a good storage for your machines when you are not using it. It will keep the dust out of your machine. Also if you don't sew a lot, only for the occasional craft or project, a carrying case is a great storage for your machine.
Now when you are an avid seamstress, you will probably have a machine that is in a cabinet. This just makes sewing easier for you because it is always ready when you are. A lot of the cabinets are beautiful and make a really pretty piece of furniture when they are all shut up.
A lot of the machines now-a-days are computerized. Learning these may take a little bit of doing, but when you are sewing a lot and doing many different stitches, these machines are great to tell you what foot to use with what stitch or you can just look at the little screen to see what you are doing.
It just depends on where you are in your sewing experience as to what type of sewing machine you should be using. If you are just beginning, you probably don't need a real fancy one until you are sure that you really enjoy this as a hobby, so I would definitely recommend cheap sewing machines. If you are quite the seamstress, you probably will want a fancier one that you can do more with and make more elaborate projects and crafts. Choose your machine to fit where your capabilities are and it will serve you better.