Making use of Difficulty Settings

I've recently resubbed after an absence of many issues and one of the new features is the difficulty settings.

Leveling my new KM/WP Scrapper (as a villain - whee!) I started to get bored and bumped up to +1 my level, then +2 my level. Aside from -Recharge foes, that worked just fine up to 30 (so far). Then I saw mention that the +(heroes) counter gave better drops vs the +(level) counter, and since my Rise to The Challenge feeds off of minions I figured I'd try that. +0 level/+1 hero wasn't a problem. +0 level/+2 heroes was good most of the time, but certain foes (Wailers, Longbow) dropped me way too fast if I hit a swarm (2-3 spawns). (Still in the early 30s)

I'm currently at +1 level/+1 heroes. Yes to bosses, no to AVs. I solo content almost exclusively. I like to have a mild tactical challenge without requiring a lot of work and definitely without grind. (i.e. I should be using Inspirations to make it through, but shouldn't be burning through them so quickly I have to manually refill after every mission). Farming is NOT interesting to me.

Once I hit 35 and start tapping into IOs I expect I'll bump it again, but I'm not sure I understand the best way to achieve what I want. It looks like I'll be going +2 level/+1 heroes as my next bump, because that gives good XP, a level of challenge, and still a decent # of drops, but +3 level/+0 heroes is also an option.

What is the "normal" progression people follow when leveling solo? Do teams have different expectations?

Without knowing an awful lot about what you enjoy, I'm not sure we can answer, because there's honestly no "typical" approach to this. It varies from player to player and character to character.

I can tell you a few tidbits I use that may help you decide what works best for you.

To consistently fight at a level setting of +2 or higher, you are going to want strong accuracy slotting (on the order of around 60% IMO), something that gives you +toHit (or debuffs your foe's defense) or both.

+2 foes are, in my experience, some of the best reward/time across the widest array of my characters. Higher than that and they start to become hard enough to defeat (and begin to lay out enough damage) that I have to slow down. Some characters with very strong area effect attacks can break this rule of thumb.

More foes tends to be better reward/time if you have area attacks to use. If instead your character is more focused on single-target attacks, you may actually do better with fewer, higher-level foes.

I don't believe there's any clear expectation of how to set these on teams. Just to make sure you're clear on how the settings work on teams, the mission owner's setting controls the level of foes, and the number of foes is controller by the greater of the mission owner's settings and the actual team size. So a team of 6 players on a mission set to x4 is going to get 6 players' worth of foes. A team of four players on a mission set to x6 is also going to get 6 players' worth of foes.