Three categories get compared as though they were points on a scale. They suit genuinely different situations and the deciding factors are practical rather than technical.
Conventional hybrid
A small battery charged by the engine and braking. Never plugged in. Improves fuel consumption substantially in stop-start driving and modestly on the motorway.
Suits: people without home charging who do a lot of urban driving. No behaviour change required.
Plug-in hybrid
A larger battery giving limited electric range, plus a conventional engine for longer journeys.
Suits: people with home charging whose daily driving fits within the electric range but who regularly take long trips.
The catch is that it only delivers if actually plugged in. Real-world data shows many are driven mostly on petrol, which makes them worse than a plain hybrid because of the extra weight.
Fully electric
Suits: people with home or workplace charging, which is the single biggest factor. With overnight charging, the ownership experience is better than either alternative and running costs are substantially lower.
Without reliable charging access, it is a compromise that depends on public infrastructure.
The deciding questions
Can you charge where you park overnight. If yes, fully electric is likely the best option unless you regularly drive very long distances.
If no, a conventional hybrid is usually the sensible choice, and a plug-in only makes sense if you will genuinely plug it in somewhere.
What matters less than expected
Maximum range. Most driving is short, and a car with adequate range charged at home is more convenient than one with huge range charged in public.