All I know from recently replacing some radiators is that all well-known brands are pretty much the same.
The crucial thing I was told is to make sure they have 'fins' - i.e. a kind of zig-zag of metal attached to them - apparently this makes them much more effective. The old ones I replaced were single-leaf with no fins - apparently these heat mainly by radiation of heat, which is very inefficient, whereas the ones with fins are better because they use convection i.e. cold air is drawn up through the fins and heated as it passed between them.
I got Barlo ones and they are fine - just your bog-standard radiators really!