As long as it sounds good, the software doesn’t have to be expensive or flashy. Perhaps the best example of this is Zebra by u-he. Hans Zimmer used it for much of the Christopher Nolan Batman trilogy. Admittedly, he did ask for some extra filter features that aren’t in the regular software, but in my experience that’s a relatively small difference from the one you can buy easily. I’m not sure if the Dark Zebra version is still available, but it was for a while.
I think iris2 is underrated! If you have the time to create your own sounds, a modular synth like Voltage is pretty cool. For canned sounds, it's hard to beat Omnisphere. But I also like to combine things, like sample a synthesizer and mess up the sound with DSP - very satisfying
The original sound can be anything. I have fun stuff from Arturia, NI and SampleTank. A search for "best free plugins" will always bring up something fun. Craig A turned me on to Pianoverb, I have dabbled but there is a treasure of coolness just in that one plugin.
Give me a sound and I will make something out of it. I may enhance it or I may create something unrecognizable - I made a cool shaker out of a kick drum from Studio Drummer once but that's simple.
Make a track, copy it, paste in multiple instances in separate tracks. Pitch shift, reverse, modulate, reverb, delay, EQ, distort.
Automate your tracks and create an ever-shifting piece that the supports the build of tension and release. 19 cents flat on one side and 17 cents sharp on the other with thte original in the center will make anything huge and ethereal. Yes, I like prime numbers. No, I don't know why!!! :- D
Oddly enough, its the software Korg MonoPoly and AAS Chromaphone 2 that do it for me. The Korg has four oscillators, so its interesting to tune them to various intervals that just three can't quite reach. It requires care to avoid weird artifacts, but the voice is available in full polyphony, so its range well-exceeds that of the original. I had one, so the software version is like something out of Star Trek. Chromaphone is a physical modeler with a very up-front GUI, so bending the model for cinematic purposes is surprisingly easy. Percussion is a snap, but the bowed variations really show off its inner weirdo. Its like having a personal Harry Partch orchestra full of perverted organs, giant metal cellos and Cloud Bowls. You can make any synth do colorful gymnastics, but for me, these two have bigger muscles from the outset.
u-he is still selling The Dark Zebra as an add-on SoundSet for Zebra2 and it requires a license. It also includes the Darker "skin" and the mods they did for Hans which give you a ZebraHZ engine as well. On my short list.
I just picked up Iris2 by iZotope a short while ago when it was free when I bought Ozone 8 and haven't had a chance to crack it open and play with it yet. As Craig also mentioned, for "quick, grab a preset" type of workflow where you are up against a deadline, Omnisphere probaby can't be beat. There are days and days and weeks and weeks worth of stuff inside that box to explore.
I saw Straylight on NI's website while trying to decide to upgrade Komplete, and it looks promising. I may need to look into that further. I personally don't do film scoring, but I use that sort of stuff for my ambient tracks. Looks like it's standalone and not a part of Komplete 12. One other go to I use for granular type stuff is PadShop Pro from Steinberg. I've gotten some other worldly textures out of it consistently.