I have some of the 30rd steel magazines with these features:

Grey park, black follower, unmarked floorplate, 'England' sticker.

Are these the same as the SA80 magazines? What are the Singapore magazines like? How can you tell these types of 30rd steel magazines apart? Which are the best?

I have both and they are indistinguishable other than the label.Brit mags can some times have problems with the catch hole although I have never experienced these problems.I have a 5 pack of the singapore mags and they are great just like the brit ones.The brit ones have a dark navy follower while the sigapore are charcoal dark grey and the are cheaper at $55 from ohio rapid fire I beleive.I got mine from a local dealer whos a friend so I didnt get gouged.

got several of each; indistinguishable from one another(other that the sticker)

yes; the same as the english ones; the sticker; have had no problems, but i try not to buy anything made in SE Asia(expecially china, korea or taiwan)--buy the england ones

Quoted: i try not to buy anything made in SE Asia(expecially china, korea or taiwan)

None of those countries are in SE Asia...

I think there might be a commercial tie between the English mags and the Singaporian ones; Chartered Industries of  Singapore is somehow related to the Brits... maybe founded by expats or something.

Quoted: but i try not to buy anything made in SE Asia(expecially china, korea or taiwan)--buy the england ones

Someone needs a geography lesson

plus, those three countries you named are probably the three most technologically advanced, with Japan on top, why would you "especially" not buy from those countries?  I mean I can understand not buying foreign goods in general, but why those three countries especially? Doesn't make any sense. 2 of them are our allies to boot.

Quoted: I have some of the 30rd steel magazines with these features: Grey park, black follower, unmarked floorplate, 'England' sticker. Are these the same as the SA80 magazines? What are the Singapore magazines like? How can you tell these types of 30rd steel magazines apart? Which are the best?

Nope, those are either AR18 or SA80A1 mags, not the new 'HK Improved' style...

However, it won't matter, as you'll be able to get as many new 'current design' USGI mags as you want in 2 weeks...

Either make good range mags.  But I wouldn't use them for defending my life if I had USGI 30s available.  These steel mags are park'd on the inside which would likely cause them to jam more easily in sandy environments.