I like metal bobbins BUT I have a Janome and the dealer said I can not use them in my machine because of magnetic stuff and the programming of my machine. So I use the plastic.

What is most important is that you use the bobbin that are recommended for yiur machine! They are recommended for a reason by the manufacture. I have a Singer that takes 15J bobbins not the 15. The 15 will work in the bobbin case but they are a little loose. 15J are more expensive but that is what Singers recommends. My Brothers uses a specific metal bobbin that is not avaliable in plastic but I have never tried to use a different number either plastic or metal. I have used plastic in my singer and really do not see much difference between the metal vs plastic as far as durability.

My Baby Lock recommends the clear bobbins so that's what I've been using with no trouble.

i have used the plastic for years because that is what came with my machine. I had a problem with just one bobbin that got wobbly then the side broke off. Other than than, smooth sailing.

my old Kenmore uses metal bobbins, my Janome uses plastic, have never had one break ... I like the plastic because they are clear and lightweight.

I use what is recommended for each machine. Have had no issues with metal or plastic.

Bobbins
 

Plastic bobbins came with my newer Singer. Metal with my 401. I'll use the kind that came with the machine. Easier to keep track of. Spent some time yesterday winding bobbins and attaching to spools of same color. Trying to keep them organized.

I am careful to use whatever bobbin comes with my machines. I can't remember ever breaking a bobbin (knock on wood here); but my machines are all in cabinets that have the bobbin holder thingy in one of the drawers; so that is what I am good at doing when I am sewing at a particular machine--thread color is not so important when I am in a hurry, just the right bobbin. I have one machine that will use plastic or metal bobbins; that is a 201, I think. I am a picture of OCD when I am teaching someone to sew on one of my own machines--making CERTAIN that he/she is aware of using the right bobbin in that machine. Plus, IMHO, speed sewing might be a matter to consider here. I am not a speed demon on any of my machines. Just my take on this subject this morning.

My machines are older. The instruction manuals have NOT specified what bobbins to buy. Wish they would have. The pfaff dealer sold both plastic and metal bobbins for my pfaff 1731 (a late 1980s macine.)

Also wish the the manuals would state what type of shank the attachments should have. (Low, high, super high)