This can be tough. Which one has higher cp? With a one stat point difference often times a lower iv mon can have higher cp due to attack being weighed heavily in the formula. That being said, I'd power up whichever one is higher cp. If it was me I'd hope it was the 98% because it would always bug me to know I had a 98% sitting there I didn't power up... but that's just me personally being weird :) They will perform almost exactly the same so really just ask yourself what makes you feel better when you look at that mon, knowing it has 98% ivs or knowing it has a bit higher cp? I'm kinda glad I don't have to decide myself hahahahah!
Yeah the gamer in you feels it should power up the 95... If you'll always look at that monster and think about that one extra point, just power up the 98 when the time comes to decide. You can't put it in gyms, it's your own personal pokemon trophy, you should enjoy it in the way you want to :) I wish I had either of those Lugias honestly! I agree with people saying to wait til the 31st to see if you get a better one, but seriously what are the odds? The thing is hard to catch as it is much less getting 100 ivs? Stop torturing yourself and power one up, it'll feel nice! :)