Rio is incredibly overrated on this forum, he had a lot of presence about him but his ball-playing skills are overhyped. He had a tendency to look good on the ball without being particularly great, also loved to play a long hoof to nowhere.
I've always pegged Vidic as the better defender of the two even if he didn't look as classy, but his strengths were tailor-made for this league. 08/09 season, he made Jonny Evans look like a world beater next to him. One of the most dominant season you'll ever see from a CB. His 2010/11 season is also under-rated.
I'd place Rio above Terry because he was more complete but Terrys longevity has him in for a great shout, he was on his last leg during Mourinho 2nd stint and still looked quality. My Top 5 would be:
1. Vidic
2. Rio
3. Terry
4. van Dijk
5. Kompany
van Dijk has only won 1 PL but I don't think any defender has had the season he had in 18/19, deserved to win Ballon d'Or that season. Looks very dominant still. Kompany is same, he was a quality defender for Man City when they started to win stuff. Great leader too