My take on placing of gems and strategy.
Take Reality (yellow) first, this is a shot multiplier if achieved. Don't worry if you dont get any portal locks from combos, as portal locks get harder to achieve as you progress save them for later.
Spin the disc, to light all shots, then start Thor mb. 3 hits to captive ball.
Once completed place gem on Hulk/ left orbit.
Play Space (purple) easy to complete, right orbit - left orbit x3, but you have a shot multiplier on the left orbit.
Place this on Black Panther/right orbit.
Then go for some portal locks via combos.
Next play Mind (blue), assuming you start with more than 1 ball from portal.locks focus on trying to start Iron Man MB, as having to hit the spinner 4 times, then the sanctum target puts your ball at risk.
Once completed place gem on Black Widow/ centre ramp.
Then Power Gem (red) as the finish is on the Hulk you're getting the benefit of shot multiplier.
You want to place this on Captain America/ through pops- for 2 reasons. Firstly it's a pain to power up, Power gem holds your progress. Secondly, when you do decide to use the Space gem to rotate the gems clockwise, it moves the Reality gem in to the place where the Power gem was meaning the shot is additionally multiplied.
Finally Time gem (orange) both ramps then lit drop, try and play this with portal locks or another MB, Thor wont be too many shots away, especially if you e got the power up from Black Widow.
Place this on the drops.
Don't worry about the when you play the Soul gem, otll likely be after your first or second gem depending on how well the MBs go. I ALWAYS place this on Captain Marvel (on my Pro) as it's an easy collect, plus it doesn't really add much in normal play.
Some other strategies if you're not going to get all of the gems.
1) If you have the mind gem, choose which gem you go for next based on which shot it is on to give you the most help.
2) Place the power and reality gem next to each other, with the power on the right, that way when gems rotate you're moving the reality gem to a high powered shot.
3) Previously MBs weren't worth that much on their own (but 0.94 they are worth more) so focus on the gem shots, if you've collected the gem focus on the disc and drops as starting times modes can be VERY lucrative and moves you towards Computer Frenzy.
4) As previously said, ignore Gamma ray UNLESS you have Reality gem on a high Lvl Hulk, then go for it, I've had over 60mil from Gamma alone.
Taking a portal lock into a gem not only awards double or triple scoring, but completing it with more than 1 ball still in play gives you victory laps, again worth huge points, so consider starting one of the other MBs alongside to prolong the MB, as there are 2 add a balls to be had from both IM and Thor MB, 6 ball MBs are not uncommon.
Using these strategies, my best score is 2.5 Billion