I always wondered why the RLM pushed so much flawed designs. The He-280 is not that bad, but it would depend on the HeS-008 radial jet engine, which wasn´t produced in numbers. Why it could be also fitted with either BMW-003A or Jumo-004A/B it´s performance would be decreased also. The decision to take the more advanced Me-262 into production is maybe right but why it never got the Heinkel ejection seat I will never understand.
Even some of the ´46 fighter planes were highly flawed:
Ju-EF 128, the air intake was a risk, wing geometry is suspect to be unstable (esspeccially without tail)
Ta-183, while a good design it´s wing without slats and wing boundary layers as well as the high set tail is expected to have very worse low speed handling (and good high speed handling)
The He-343 as well as the Ju-287 are looking quite promising, just as the Me-P1101 looks.
The best offensive jet plane in my view would be the Ar-234 C, but only 14 of these fast jets have been produced beside of some prototypes.
The best defensive could be the He-162 against fighters (also allied jet fighter) and the Me-262 against bomber.