It depends on what your preferences in story are. Ninja Love, if you ever plan to play that, tends to have spinoffs that end with the characters doing kinky smut stuff by the end. I personally really liked every Magic Sword spinoff. The ones available in the free version are longer than I'd have expected, and the one with the haunted mansion only has Wounded Hero Checkpoints.

I'll go down my mental list.

Destiny Ninja: Cute and almost all have smut and CGs attached. The endings are shockingly short, and if you only come back to the spinoffs after a long time because you needed enough for a checkpoint, it's easy to forget what even happened. Sometimes it is anticlimactic.

Angel or Devil: Some have CGs, and most of the spinoffs can be played whenever if you don't have enough items. That said, some spinoffs have steep requirements, so replaying is a pain.

Lost Island: Rather slice of life. Not much happens after they flee from zombieland, so they're just going on dates and parties and whatever.

Mononoke Kiss: There are a lot of spinoffs. Most are rather casual and play on foreign traditions that the characters suddenly want to partake in. There is currently a campaign in this game, so all of the previously limited time spinoffs are available again. My favorites were the ones about the characters' pasts, and they have CGs.

My Fairy Tales: I like these, but Sweets requirements are stifling when you need them for the main route.

My Sweet Prince: Most of the spinoffs are extremely short, and you need a lot of Keys, of which the type vary between spinoffs. The longest ones in the free version are the sequel ones, they have CGs, and they are limited time.

Ninja Assassin: I've liked all of them, but all of them so far have been limited time with significant Purse requirements.

Scarlet Fate: Only two spinoffs (sequel stories) exist in the free version so far.

The Niflheim: The only free spinoffs are sequels, but they are cute and not limited time. You need to buy a lot of avatar items, however. It makes you ache for Closet. No idea about the current spinoffs that cost money.

Oh, I never answered this. Well, I only play spinoffs in My Sweet Prince because I completed all of the main routes, so I'm only logging in and doing training when spinoffs and campaigns are not happening. I also have not played My Fairy Tales in months to stock up on items and Gems, and spinoffs are exist forever in that game. I'm not really pressured. I waiting for the new route to finally appear in Ninja Love (finished almost every main story ending between the + and GREE versions), so I have also stalled in this game.

For the games that I am truly balancing, I usually stick with one character until I don't have enough game money to proceed, and then I move to another character. Once I have the right amount again, I go back to the other route. Once I complete that route, I replay from the beginning, fast-forwarding. Since there are commonly three endings per character, I have three chances to read and refresh on whatever happened in the main route, anyway. Wizardess+ and Niflheim+ are infinitely easier to pass without deviating into other routes, so once I finish that route, I repeat the same character's route and only fast-forward until I get to the different choices/ending. Since I am typically repeating the same stories whenever new spinoffs are not happening, it often leaves me with only a handful of games where I am reading new material. So it all goes in a cycle.

The only problem for some people is that they experience story amnesia if they change routes, so they have no idea what is happening by the time they get back. Thankfully, I usually have some memory of what was going on. It also helps to have the story save tickets in certain games, so if I really am too busy, I can just skip over the entire section and save it for later. Even though I'm always complaining, I guess this shows my patience. Totally refuse to spend money unless I buy an actual game/route in a non-free game. I have even amassed enough items in some games where I can probably complete the majority of routes in one go. Buuuut I just wait for spinoffs.

It is rather ridiculous knowing that as the commercially hyped up holidays appear, almost every free app suddenly decide to have events. That is the only time I really struggle, as I screenshot everything for myself as I go, which takes double the time of simply reading a main route that repeats over and over, and it is all new stories.