I've used both the metal blades and abrasive blades on a circular saw, and don't recommend either unless that's the only tool you have.
Cut off wheels work well. And the thinner, the better. I use a air powered die grinder , but it's rated at one hp, and will cost you about a grand, the cheap ones will work but will bog down and be slower, and then again you will need an air compressor that will keep up with it.
Your best bet it to get a good angle grinder, 8 amp or better. 100 bucks will get you a decent one. Then you can run a 5" or even 6" cut off wheel all day long.
Just be carefully, the thin ones cut fast, but if you get them in a bind, they can shatter and fly at you. Always inspect the wheel for fractures before using. They can get a bend in them just from setting them down wrong. Wear eye protection and gloves, long sleeve shirt. Face shield if you have it. And don't ever work in shorts or open shoes!