Your power up strategy? Many or max?

many
I want my mons to be useful to the last in the raids that i target. once i have all my main squads sorted to level 30 then I'll start pushing some higher.

I've always maxed my top Pokémon but now a stardust shortage, I am going to be even pickier on which ones I do max. Due to gym raids, I may bring a high IV/good moveset machamp and tyranitar (B/C) to lvl 30. Already have one B/C ttar maxed, a SE one maxed and a DP machamp maxed. Not 100% sure tho kuz stardust may be going to legendaries instead.

Many to 30...as a rule.
Occasionally a max...but for no other reason than I just want to max that specific mon.

Many. I want at least 4 level 30 strong Psychic, fight and rock. Will move to ground and possibly dark after that. My first priority is soloing level 3. 2nd priority is max damage against legendaries

I mix both. Powered few of my most useful mons to lv 33 (right at the border after which costs start to skyrocket) and keep a bunch on lv30. After few failed attempts to solo Lv3 bosses (except for Machamp) I came into conclusion that lv30 are not strong enough to finish raids in time / before fainting. Higher levels are mandatory for at least 2 mons in an attacking group.

I tend to take many to 30 rather than maxing individuals out. As others have said, stardust is scarce and the investment beyond 30 is significant. If you're swimming in dust, go for it; otherwise, I'd say take as many to 30 as you can.

I have maxed out some Pokémon (to level 35.5):

Alakazam PC/P 86.7%;
Snorlax ZH/BS 93.3%;
Dragonite DB/DC 93.3%;
Blissey ZH/P 82.2%;
Golem RT/SE 89%;
Exeggutor ZH/SoB 100%;
Vaporeon WG/HP 93.3%; and
Jolteon TS/TB 97.8%.

Have others level 33.5 32.5 and many others level 30.

I've got probably 50 guys at level 29-31, but only 5 higher than that and that was back when we were getting 5000 stardust a day from gyms.

Now I hardly even get them to 30. I checkout the most likely counter targets for that particular mon then see where the attack rounding gets me the extra point on the fast move and stop. So my Ttars are at 30.5 instead of 31. My dragonite is 29.5, others I've stopped at 28.5. It's such a pain to level guys now that I look at my lev 34.5 Donphan and laugh.

My best attackers - 3 d'nites, tyranitar - are maxed to 37.5, but there are other, previously less useful mon (e.g., espeon) that I am currently trying to get to 30.

I'm not investing in defenders right now, but have a lot of good ones already that will cost enemy teams potions ;)

I just basically evolve everything that's already at a high-enough level and max out a few "special" ones such as my only Dragonite and Espeon.