Iv or CP?

Your decision

Higher IV means higher max final CP

Is it a mon that you plan to use in battle, or a DeX filler? Do you have enough candy and dust to get the 96 to the level you want? Do you already have one of the evolved form? Is there a specific raid boss that you want it for right now, or can you wait? Is it the best species of it's type, or are you likely to get a mon that will fill it's role better in the future?
So many factors go into the decision.

Depends on the Pokémon. For Example I have caught a decent IV level 35 Chimchar with 14 attack. Since Infernape is not meta-relevant at the moment, and I’m not going to waste stardust on it, then I’m going to evolve that one to play around in gyms and what not.

However, if you have something like a Gastly or a Machop that you are eventually going to power up for raids and such, I would go with the higher IV. Having a full team of Machamp for gyms and raids (or gastlys for Mewtwo and Giratina) will be worth the stardust in the long run.

Is this a pokemon you intend to power up?

If it's a meta-relevant pokemon that you're willing to spend stardust on powering up - then evolve the 96% for sure. It'll make a noticeable difference to it's CP (and fighting ability). For example, a level 35 Tyranitar with 15/14/14 IVs would be 3392 CP, whereas an 8/7/8 IV level 35 Tyranitar would be 3205 CP. That's a 187CP difference at the same level - or basically the 96% Tyranitar is as good at level 31.5 (3210 CP) as the 50% is at level 35 (a 3.5 level difference).

Now, if it's a pokemon that's not worth powering up, then may as well evolve the one that's already at a high level. Let's compare evolving a weather boosted level 35 50% IV Hariyama to a level 18 100% Hariyama: 2377 CP versus 1422 CP. If you're not willing to power it up (I wouldn't spend stardust on a Hariyama) there isn't much point. Meanwhile, the level 35 50% would still be useful in Tyranitar raids (and any raid weak to fighting) until you have a full team of Machamps.