I nearly always use an adjustable piercing saw, which I much prefer to the fixed kind (but opinions here do differ).
I started with a selection of blades from Cousins, their own brand are German made and work perfectly well. They are not expensive but you will break a few (particularly at the end of a cut). Don't start with too fine a blade.
Most recently, I treated myself to some of their 'Valorbe' blades – which also work perfectly well but I'm not sure I can really tell that much difference between them and the Cousins own brand – although there might be a slight edge in smoothness of cut (or it could just be my imagination). Both types all cut well enough though and also seem to last OK – at least until I do something daft of course…(like losing concentration)
I've learned not to skimp when it comes to buying cutting tools (like hacksaw blades, files and piercing saws). I've used quite a few Cousins products over time and they are generally reliable and not that expensive. I'm sure there are other good suppliers around but that's where I get this kind of thing from (I'm just a satisfied customer – no other connection).
Regards,
IanT