I agree on the He 280, perhaps if Heinkel had gone with a more conservative development of the aircraft and Ohain hadn't abandoned the earlier HeS 6 (which while somewhat bulky and heavy, was no larger than Whittle's engine and only moderately heavier then the HeS 8 at 420 kg) It was already producing nearly 600 kp thrust when it was abandoned in 1939 and had far fewer problems than the HeS 8. Additional improvements would likely be possible after aquiring Hirth.
They would have had to mount it mid-wing with a curved spar similar to the Meteor and it would have been wise to make more provisions for fuel capacity. Weapons capability was dencent, in fact the Me 262 had originally been designed for 3x MG 151 as well, though it proved capable of much more, the He 280 could probably have been upgraded to 2x MK 108 (possibly 3) without much trouble.
The biggest mistake Germany made with Heinkel's jet program, and possibly the biggest mistake of the German jet program, was the cancellation of the excellent HeS 30 (109-006) in 1942 when it was making great progress, considering the 004 and 003 "good enough" and assuming the latter two were nearing production at this time, while in reality they would both be stalled several times (particularly the 003).
Heinkel-Hirth instead was forced to move on to the "Class II" HeS 011 which developed somewhat slowly and was still in the prototype stage at the end of the war.
The HeS 30 was equal or superior to all other engines tested in the war in terms of specific fuel consumption, thrust/weight, and thrust/frontal area. And no individual engine beat it in more than one of of its categories. (the 19" diameter US J30 had better thrust/frontal area, the Nene had better thrust/weight, and I think one of the Metrovick engines had better SFC)
It may have been a case of both "good" and best, not being overly complex and would probably have been easier to produce then the 004 (probably not quite as quick to built as the 003) and could possibly have been ready for production before the 004B. (and certainly before the 003)
Had the Me 262 used it, it would have been ~1,600 lbs lighter (with same fuel and weapons load) had ~40-50% longer range, better engine handling characterisitcs, better speed, climb rate, and maneuverability (particularly roll), a shortened take-off run, and better low speed handling.
Then again you could also say that when the Jumo team (working on the conservative 004) merged with the Junkers jet team (with Adolf Müller) with several designs on the drawing board and a test bed engine constructed (what would later become the HeS 30 was the least complex of these), they should have dropped the conservative Jumo design and developed Müller's engine.