Hmmm, there was no one real answer to the question.
The Eheim 1250 is about as good as it gets from the Eheim range. The larger Eheim pumps dump too much heat into the water without increasing pressure/flow enough to offset. Eheims are submersible, reliable and quiet. The Ehim 1048's do offer very good performance for small closed loop systems though.
The Danner Mag 3 is perhaps the best balanced pump of their range. It does have some realibility issues (impeller housing cracking from some reports), but it's cheap and possible a better "balance" than the Eheim 1250.
The Iwaki MD-15R for 60Hz (USA) is possibly about the best tradeoff for flow/pressure/pump heat. For 50Hz countries the Iwaki MD-20R is good for low restriction setups, and the MD-20RZ is good for moderate to high restriction setups. Iwaki pumps aren't submersible though.
The main problem here is selecting a pump for your needs, and over the range of pumps listed above we're probably talking less than a 1C difference in final temperatures as a result.
If you wanted to simply choose the "best one-size-fits-all tradeoff", and you lived in the a 60Hz electricity country, and wanted quality, then the MD-15R would be my choice, but it is expensive. The Eheim 1250 would be next if you wanted quality over cost, and the Danner Mag 3 at the bargain basement near performance equivalent (but greatly reduced quality) of the Iwaki MD-15R.
For radiators, the biggest radiator you can get is pretty much what you want. Of course some radiators are more efficient than others, but it all depends on your space requirements. If the question was "What's the best radiators that fits is X amount of space" then people may have a chance of answering it for you.
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