I mostly end up playing chogath or taric. Currently i have a mix of flat and level cdr glyphs which im looking to change since .. well they feel fairly lame and early game, they are way too useless, while late game, i usually get the 40% cdr anyways so they are a total waste. I tend to play hybrid caster/tank or dps/caster depending on the teams.

So question is now... mpr/5? or mpen? mr? or does anyone have better suggestions? my problem with mpr/5 glyphs is they are reallly really slow.. 0.31/5 flat glyphs seem totally worthless as a full set gives 2.79 mana/5 seconds.. just over 0.5 mana per second.
my other consideration has been mpen.0.57*9 = 5.13% which seems.. decent considering its a flat 5% more magic damage. (this is what im leaning towards so far)
the other choice would be MR for 1.49*9 = 13.4% more effective hp against casters which doesnt seem bad either. i thought about mixing them but i dont think it would be too noticable for either.

the other thought was to get flat mana runes. 11.25*9 = 101.25 mana.
but thats only worth 200 ish gold and only gives me one more cast of something.

Don't be so quick to write off cooldown reduction runes. Between glyphs and masteries, it's possible to get around 15% total cooldown reduction, which means you only need a single 25% item to put you at the cap (like Frozen Heart).

As for mana regeneration runes, if you're going to use them, the per-level ones are the only way to go. The flat ones are worthless; you break even by like level four. A full set of tier three Clarity is 0.9 mp/5 per level, which is nothing to sneeze at. Dodge or magic resistance might be preferred for tanks anyway, of course, depending on how you want to play them.

well most of the time i tend to play hybrid since AS on cho hugely boosts his damage between his pretty godly base damage and his WHOMG vorpal spikes damage which is boosted further by AP.

my builds contain rylai's 80% of the time. as vorpal slow is basically the same as having frozen mallet but also boosts rupture, silence, vorpal, and feast damage.

but basically if i ever play tank, chances are I get ranudin's+ nashor (which is the full 40%), or ranudins + soulshroud which tends to be plenty or ranudin's + frozen heart. as taric all are equally likely. heck.. as taric most of the time i find it hard to choose between items because i already have the full 40% but want to use another item which still has CDR on it.. typically against DPS (AD/AS) heavy teams ranudin + frozen heart + soulshroud is kinda common for me even though its wayyy more than the cap. which is why im asking.

usually im out of mana (and or dead) rather than dying before my mana pool is empty since most of the cds on Cho and taric are fairly low. mana tends to be a problem but as taric i take clarity (sometimes at least) and i tend to take tear.

my full page is Apen/dodge/CDR (half flat half /level) 2x health quints + 1 move speed quint. between boots + not getting nashors, i tend to end up with zeal, either lichbane or leviathan in some cases both and it helps both chars be able to chase for stun/popup/feast. as my playstyle is fast tank/support, get in, cast, tank a few hits, get out so i dont get focused entirely.

anyhow, yeah. thanks for bringing that up. i totally missed the mpr/5/level runes. those are much more in line with what im looking for. I just feel way too squishy early game against the likes of ryze and viegar and nidalee that i would consider MR runes or.. Mpen to kill them before they kill me. but i dont see that happening much as they have much better burst and are basically AP only. I guess i will be trying the mpr/5/level runes for now since they are cheap, then work on Mpen/MR as i get more IP