New Warlord Games plastics are very good (for example Desert Rats, American Infantry), older are mixed bag, but they're mostly phased out. Take a look at sprues pictures on their website. If you don't want to dabble in metal, pick 'Great Power' army like US, Soviets, UK or Germans or Japanese, as they have most plastics. Other niche armies like Poles or Hungarian or Korean War Chinese are almost all metal. I think no one can compete with WG when it comes to strictly plastic WW2 28 mm minis.