Who's greater? Nobody can even agree on what "great" really means in the first place. So what is it that you're trying to rank?
But let's be realistic about one thing: if you were building a modern team you'd have to pick Jordan over Russell.
Yes, Russell was dominant in his era, but it would be disingenuous to pretend that players haven't gotten better, faster, and stronger. And yes, that's skill-wise as well.*
*Somebody is inevitably going to disagree with this statement because they don't understand statistics, so I'll preemptively respond:
Let's start with the underlying fact: far fewer people played basketball in the 50s and 60s than today. Not only was the population in the US smaller (and it wasn't played internationally) it was simply less popular than it is today. Erego, it's undeniable that far more people play the game today.
After establishing that underlying fact, we make one assumption: that players in the 50s/60s trained and practiced as hard as modern athletes. In reality, this is almost certainly untrue. Very few of them even lifted weights. But I'm assuming it's true to give the benefit of the doubt to the 50s/60s players. We make this assumption in order to establish a ground of comparison where the only difference between the eras is the number of players that the league is recruiting from.
So we draw our conclusion: ceteris paribus (all things being equal) the fact that the modern basketball players are drawn from a larger pool means that they are more likely to be rare specimens of special talent/size/strength/ability.
Since my point might not be entirely clear I'll make an example. Say you had to make a basketball team out of the first 15 people you see. Your recruiting pool is very, very small, and you're stuck with what you've got. On the other hand, I'm allowed to select from the next 1000 people I randomly encounter. Now, unless you happened to be very lucky and you're hanging out in a college basketball gym as you read this, I'm probably going to be able to create a much better, taller, faster, stronger team since I have more options to choose from. That's the modern NBA, while your situation is NBA of the 50s/60s.
Statistically, the larger the pool of recruits the better the elite athletes will be.
And obviously, this applies to talent level as well. If I have each of my 1000 recruits shoot 100 3-pointers you better believe I'm going to find a couple of budding Ray Allens in there somewhere. You'd be lucky if one of the players out of your 15 can even hit 3 pointers at a rate of 25%.