Switzerland has to be top of the list, but not specifically 'SBB'. Switzerland is IMHO unusual in respect of the thread title in that you really have to take the 'Swiss Travel System' as a whole rather than an individual operator. Integrated, multi-mode (everything from marked walking paths to water transport to high mountain top cable transport to high speed line trains is connected) and multi-company operation, frequently on or close to right time, taktfahrplan system with 3 - 6 minute official connections so no hanging around (and services frequent enough that even if they have to break an 'official' connection 'there'll be another one along in a minute'.
Add to that the 'route' fares system whereby (with a very small number of specialist exceptions) a normal ticket is valid for a route not a type of train or specific railway operator.
In Switzerland it matters not one jot what type of transport turns up to take you from A to B. For example on Zurich to Chur you can get on an SBB Intercity hauled train, SBB double deck semi-fast EMU, SOB Traverso EMU, DB ICE set etc to undertake the same journey. Even where trains have been replaced by buses, the buses line up right outside a station, or even adjacent to station platforms in some rural places.
If something untoward happens, 'the system will get you there', for example a while ago a cable railway to a mountain town was under repair and a replacement helicopter service was provided for residents. Following the recent flooding, the only links completely broken are those where the parallel road has also been washed away.