What is better?

Worth a read:

https://www.reddit.com/r/TheSilphRoad/comments/7cfqj0/the_0_def_iv_myth_why_15015_isnt_the_secret_to/

What attacker?
What defender?
What levels are they?

There are no generalisations for IV that will hold true all of the time for all mons in all situations.

Guess it depends on what you value more: lasting longer, or more charge moves. Although there really is no difference at all between those IVs.

100 99 percent of the time. Sometimes 14 stamina and 15 stamina is the same at level 40. Like take tyranitar for example, at level 40 a 100iv and a 97iv 15/15/14 ads will have exact same attack defense and hp. Only difference is cp from 3670 to 3661. On gengar tho, 14 and 15 defense there is a difference at level 40 raiding alakazam. U can take an extra confusion with 15 defense 13stamina+ which lets u fire off extra Shadow ball or 2. While 14 defense u wont hit last defensive breakpoint at 40 and will only be able to take 4 confusions. Won't be able to fire off that extra or 2 shadowball off. U might be in the middle of firing it off but u die before it registers while 15 defense let's u survive to register the extra charge move.

Almost always no. But the difference is something like 0.6% of the time. They are functionally equivalent. Lag, phone delays, tapping timing, software bugs and glitches will have a much bigger effect on the battle than a point of defense.

You would have to hit multiple matchup-specific breakpoints for 1 def IV difference to result in firing more charge moves. Damage rounding and energy gain rounding already make it so that low def IV doesn't result in more energy gain in many cases, and when it does, gaining 1 extra energy per attack taken might not translate into getting off one more charge move. The mon may die faster due to taking more damage or that extra energy might just be redundant.

If you have both IVs on a good meta pokemon, max out both. 98% is amazing, extremely rare and funtionally identical to 100% most of the time.