Arithmetic games aren't much my style either.
For paid games, I think SWD(Shall We Date) games could be played offline after stories have been downloaded, while Voltage games need a internet connection to load and play. The orientation of SWD games are portrait while Voltage games are landscape.
As for free games, login days are more important in Voltage games, if you skip logins, you'll miss out on a lot of items. In SWD, the logins give the same set of items.
Events in my opinion is harder in Voltage games. Voltage and the new SWD both have two types of events, where one features limited-time event stories separate from the main story meaning they can be read without story tickets, and the other is a collection event where you read the main story and try to collect as many items from doing so.
Completing an ending during a story event in SWD games will increase your friend limit by two and there is no maximum friend cap, while in voltage games the max number of event friends is usually capped at 11, and each unique ending completed will increase the allowance by one until it caps and will no longer increase.
One thing that may bother you about Voltage games is that they have a lot of popups that reappear every time that page is reached. Some games have the option of never showing again(no promises there) while some don't.
CG's are more easily attainable in SWD games using the old system while newer games require either spending real money or doing enough offers through Tapjoy to buy the premium items needed. CG attainability differs between voltage games.
Closet and storage space is more difficult to obtain for free in Voltage games. They will be given as prizes on occasion and can be bought using real money. Most newer SWD and all the older games have them for sale in the store for either real or game money. Some newer SWD games also have them as gacha prizes.
All SWD games refill a story ticket every 4 hours until it reaches the 4 or 5 ticket maximum. All Voltage games give 5 story tickets per day and refills at 11am UTC each day.