Are there any negatives with a bulb upgrade? (reduced bulb life, heat, fragile, etc)
The short answer is that xenon will improve the light output (maybe by 10%), give slightly whiter colored light, and lasts longer. Xenon is also more expensive, so it might not be worth it. Halogen would be even better, but you would probably have to get a flashlight designed to use a halogen bulb, since a bare halogen capsule can get very hot.
Halogen capsules can also be inconvenient to install because they should not be touched with bare hands, since the traces of oil left on the extremely hot fused quartz capsule can become charred, leading to localized overheating and rupture of the capsule.
Here is the long answer:
The addition of krypton gas to a bulb increases filament life by reducing evaporation, and slightly increases efficiency because the higher molecular weight gas is less conductive of heat away from the filament. Xenon is even better than krypton.
A halogen capsule makes the filament last significantly longer, although the iodine vapor in the capsule absorbs around 4% of the lumens (the absorbance of iodine is a smooth curve, mostly in the central greenish portion of the spectrum, very slightly in the blue, this can give halogen light a very slight but noticeable pinkish tint in some cases). If the type of gas filling allows the filament to last longer, the filament is often designed to be shorter and thinner (maintaining the same resistance value) to allow a higher temperature. The filament glowing at a higher temperature leads to greater efficiency and whiter color of light. The halogen filling just allows the filament to be designed to run at a higher temperature without burning out too fast. So to directly answer your question, typically a halogen version of a bulb will have better performance than xenon.
In general, halogen puts out whiter light and is more efficient (because the filament is usually designed to run at a higher temperature). However, operating at a higher temperature can make the filament mechanically weaker and more vulnerable to vibration. Since we are discussing flashlights, another thing to mention here is that halogen bulbs designed to use lower voltages last longer than halogen lamps running on outlet voltages, since the filaments are thicker for any given wattage.
Krypton gas helps increase the efficiency more for smaller bulbs, where the losses to thermal conduction are greater. For a 100 watt bulb, using krypton would only increase the efficiency by 4%. It should also be mentioned that a regular 60 watt bulb is still going to give off whiter light than a standard 20 watt xenon bulb. When they say xenon gives off "whiter light", what they really mean is that the light is whiter than a bulb of the same wattage that is rated with the same lifespan. Higher wattage and shorter life still make more of a difference in color temperature.
Xenon and halogen bulb versions typically give off a little more light and last somewhat longer than regular bulbs, though how much more of each depends on the construction of the filament, since there is an inherent trade-off between efficiency and filament lifespan. Virtually all flashlight bulbs use krypton, though krypton is sometimes used in certain "higher performance" regular incandescent lamp bulbs. Regular light bulbs normally contain an argon gas filling (with a smaller amount of nitrogen). If you look on the periodic table, neon, argon, krypton, and xenon are all noble gases which have progressively higher atomic weights as you go down the column.