The stars that will most likely use up their nuclear fuel soonest are small, low-mass stars like red dwarfs.

Here's why:

* Slow Fusion: While red dwarfs have a very long lifespan overall (trillions of years!), they burn their hydrogen fuel very slowly due to their low core temperatures and pressures.

* Smaller Fuel Reservoir: Despite their longevity, they have a smaller total amount of fuel to burn compared to larger stars.

In contrast, massive stars like blue giants, though much brighter and hotter, have much shorter lifespans because:

* Rapid Fusion: Their high core temperatures and pressures lead to extremely fast nuclear fusion.

* Massive Fuel Reservoir: They have a much larger mass, meaning they have a huge amount of fuel to burn.

However, this rapid burning leads to a much shorter lifespan, on the order of millions of years.

To summarize: Smaller, cooler stars like red dwarfs burn slowly but have less fuel, while massive, hot stars burn quickly but have a huge fuel reservoir.