An ACH transaction between two North American banks usually arrives on the next business day (if you place it before the cut-off time). In fact, ACH supports multiple settlements per day now so if that feature is supported by your bank ACH transfers can even arrive on the same business day. There are a few banks that are slower, but that's not the fault of ACH - don't use slow banks and you're not running into that issue.

That's very similar to SEPA transactions, with the exception that some European banks support real-time settlements for SEPA. For banks that don't support this yet funds usually arrive on the next business day.

Transfers between the US banking system and the European system are usually slow and expensive as those two systems aren't directly linked to each other. So you your bank needs to send the funds to a correspondent bank which forwards the funds to the final destination. But if you use 3rd party services such as TransferWise those transfers are significantly faster and cheaper. My last transfer from my US bank account to my European account (via TransferWise) arrived on the next business day and cost something like 0.36% on top of the mid-market rate.