Talking about AP champions that greatly benefit from cdr, such as 
.
Which page would be better for blind pick?
Prospector Pete1 votesIt really depends on the items. If you're gonna go Morello's and Athenes, then you don't need scaling CDR.
jjookkeerr1 votesthere is no reason to build both, you are just delaying power and making your build weaker mid/late
Prospector Pete1 votesI was just giving an example.
jjookkeerr1 votes15% cdr
LilxPaprika1 votesAt lvl 18 ya 15% CDR easily But the lack of ap early can severely hurt your ability to trade with you opponent and clear/farm minion waves.
Dreadlocks1 votesThis is too broad of a question, or too easy to answer depending on how you are looking at it. From a lvl 18 stand point, the 15% CDR is better than 15 AP. From a rune page perspective, the 15 AP is better. You should look at your match up before deciding what you want. Generally you could run CDR per lvl blues vs an AD. Some people/pros value CDR per lvl blues so much that they even run it vs strong APs too.
TL;DR I would think twice before running CDR per lvl on your quints. The 15AP early game is hard to match.
Also i recommend MS quints for TF :)
Rolien1 votesMost of those champs will have 5% cooldown from masteries add in the scaling cooldown and at 18 you have 20% cooldown from just masteries and runes alone. Throw in a morello or athenes and you have max cooldown from just 1 cooldown item. That allows you to build something more beneficial if you want max cooldown.
Early game the 15ap would be better but if I remember correctly at level 11 you are getting 10% cooldown from the runes alone. AP is easy to get in a game Cooldown not so much.
That's just a silver's opinion though take it as you will.
Julij21 votes15% cdr is overall better however 15 ap is better in early game. I go for scaling cdr in 90% of my matches. The only time I'm not doing it is against a matchup that I don't know or with a champion that I haven't played enough to be comfortable enough.
Tl:dr at 18 scaling cdr is way better.
Jungle Lux God1 votesThere are so many factors that go into this that there's not a clear-cut answer.
On a lot of champions 15% CDR is generally better, but at the same time there are also champions that would normally build at least one or two items that have CDR on them (even if they aren't building them for it) that makes the AP quints a bit better.
There are also champions like Karthus that don't scale well with CDR or champions like Ryze who have innate CDR that prevent them from using this effectively.
Nekusen1 votesi have a friend that mains 
and builds 35% CDR with runes (+5% with masteries) so he ends up getting full CDR without building items.
i would build penetration n' sheit though
