Slitherine

I never use strat bombers, simply because of their high costs.
Their efficiency vs cost clearly make them underperform.
I see no arguments in this thread that has opened my eyes, even when the enemy uses strat bombers against me, i focus on all other kinds of planes first.
I do believe they are designed with the idea of them being "flying artillery", but they just don't do enough damage, or reduce the efficieny/fortification enough to justify a 200+ rp cost and 3cp cost. Also, fighter will attack them and repairing them is also an insane rp drain. and the toilet is flushing enough as it is!
Another thing to consider, the enemy fields tons of AA with high rating against large aircrafts, further decreasing their usefullness.
when i have them as auxilliary of course i use them, but mostly to wear down aa so that my real bomber can have destroy them and have free reign.
I have never purchased one in over 750 hours played in the game.

I'm a tac bomber fan myself, eg Stuka and Helldiver because they're almost always guaranteed to strip at least one or two strength points off whatever they're attacking and give you a warm fuzzy feeling, whereas strat bombers tend to reduce efficiency rather than actual body count.
I'm also a fighter-bomber fan because their cannons can chew up ground/sea targets pretty good, AND also give enemy fighters a bloody nose.
(Of course if there are lots of enemy planes buzzing around in a scenario I increase my pure dogfighter strength and reduce my bomber strength)
My entire Okinawa air force is in this screenshot, namely 4x Helldivers, 1x Corsair and 2x Lightnings, the jap air force put in a lukewarm appearance early on then disappeared, but I'm keeping one Corsair as insurance in case they come back..

It really depends on the campaign. Generally, I don't use strategic bombers however they are fantastic in Morning Sun campaign. This is mostly because for the majority of the campaign all fighters and tactical bombers are garbage so stats of the strategic bomber are actually very good in comparison. Additionally, you don't have access to any decent artillery so that's another reason to use them.

I also avoided using SBs for my first year of play due to their expense, their perceived lack of effectiveness, and the need to spend skinny air CPs on fighters and dive / torpedo bombers. The considerations are still very scenario specific (particularly with scenarios Pacific), and it always seems less painful to allocate SBs in the 2nd half of a campaign when resources are higher.

obo13 lays out 3 key reasons to employ SBs in the 5th post of this thread- well worth rereading. An SB with a shock value of >=20 drops a devastating efficiency attack, which has utility in a lot of front line situations. The SBs have a superior range compared to land based artillery, and as a precursor to the follow up attacks, they break lines and take hexes. I want to be brave enough to try swapping SBs in for tactical bombers...

You can argue for the subs also, some people actually manage to use them somewhat effective, and the developers did try to make them more effective with the kriegsmarine massive change, truth to be told on higher difficulties you can not afford to use them, there are close to no enemy fortified position that does not have at least one or several aa-guns, every strength point on a strat bomber is costly to replenish, very much so. Imo i think that they should lower the cost to the price of tac bombers, and lower the shock value to 10-15. then i would consider using them, there is also supply devastation thingie, i have only seen it been effective once, and that was when a strat bomber bombed my only airfield. that hurt. else... to pricey, to much things will target them since they are "high" value units, the ai often skips fighting my fighters to go straight for the juicy targets.this might be different in multiplayer as i have little experience in that regard, but in camapaign or scenarios, i just cannot justify using them. Considering range, with a good transport attached artillery can be quite mobile, and they aren't as vulnerable to fighters or aa guns.