I'll take as much ISO as I can get.
Noisy photos might look pretty bad, but if you had to go to ISO ten gazillion to get the shot at least you got the shot. If you've got the right tools noise can be disguised as grain, at least to a certain degree.
On the other hand, blurry photos due to lack of shutter speed are pretty much useless. This is why "boost" mode for the last stop of ISO exists even though it's just a simple linear amp that has the same effect on the sensitivity as setting +1EV in the raw converter. It might be ugly but it keeps your shutter speed up so that you can get a stable shot.
Impromptu portrait, 19th century Polish Hussar's costume. Most light was from what was probably a 35 watt applique.
85mm f/1.8 USM @ f/2.0, EOS 6D MRAW, ISO 25600, 1/100th sec, cleaned up a bit in LR4.
Without using "boost" mode, I would have been at 1/50th and probably would have had a near-useless image due to camera shake. The 6D continues to blow me away with its performance at stratospheric ISO levels.