Let's start with the obvious difference between the jungles.
T1/T2/T3: Tier 1/2/3 towers. Tier 1 towers are the ones closest to the river and the Tier 3s are inside the base.
Easy/Medium/Hard camps: Refer to the image below
Credit goes to Xenasis's Jungling 101 Guide here
Mountain: The cliff below the Radiant's closest (to the base) hard camp and above the Dire's closest hard camp.
Placing a rune ward will reveal one of Dire’s Medium camp as well as movement between the medium camp and the safe lane large camp. What this implies is a common rune ward is able to detect slight jungle activity, especially an active jungler such as Chen or Enigma. A rune ward on Radiant’s cliff side, however, will not reveal any jungle activity, which is why the current trend is to place the ward at the high ground behind the hard camp (on the left of the medium camp).
Warding Dire’s mountain (right above their closest hard camp) will reveal rotations between the top and middle lane through the jungle whereas Radiant’s mountain ward will only reveal movement in the jungle between the T3 and T2 mid towers and their T2 safe lane blind spot.
When I say T2 safe lane blind spot, I refer to the fact that there is an additional route behind the T2 tower. For defensive purposes these trees are usually cleared if possible, but as long as the trees are there the Radiant side is at an disadvantage if they were in a defensive position.
River: 2 different entrances from the river for Dire, as compared to 1 forked entrance for the Radiant.
Safe lane: Partial visibility into the jungle near T1 for Dire but practically no vision into the jungle at Radiant’s. Radiant has a wider and deeper vision into their jungle behind their T2 as compared to Dire (only during the day though). Additionally, Radiant has a blind spot behind their T2 tower.
Mid lane: Movement from the jungle to the secret shop is undetectable on the Radiant side, but easily detectable on the Dire side. Note that the juke spots behind the T1 is linked to the jungle for Radiant but independent from the jungle for the Dire (which is easily accessible from the river). Dire’s blind spot is a high ground entrance as compared to a uphill cliff for the Radiant.
Off lane: Radiance’s offlane entrance allows the Dire to roam freely behind the T1s and T2s of both the mid lane and the safe lane. Dire’s offlane, however, has a cliff and a large neutral camp that slows down movement and entry is easily detectable with a simple aggressive lane ward.
Statistics show that the Dire tends to win longer games and the Radiant tends to win shorter games. From the differences listed above it is clear that Radiance has a slight edge in ganking potential early game, as their Jungle is safer as compared to Dire’s, requiring only two wards to detect entry into their jungle early game. Dire has to place three wards to fully cover all possible entrance into their territory.
However after the T1s are gone, a protected Radiant jungle is spookier than the Dire’s. Dire’s safe lane is wider and the forest is thicker and tighter, giving them greater defensive power. A single mountain ward will allow them to anticipate ganks from the two exits at their T2.
Radiant’s mountain ward defends against only one of two possible gank routes for both the mid and safe lane. The worst case scenario for the Radiant is to have Dire pushing their T2s at mid and bottom concurrently. Dire has the high ground vision advantage in the middle push, and blind spot uncertainty advantage for the bottom.
On top of that, it is more difficult to contest Roshan. Radiant need to cover a greater distance, move through their jungle and in the process passing through either the blind spots or risk moving up the high ground. The only exit leading to the Roshan pit is easily scoutable, which is why smoke is staple for a Roshan attempt for the Radiant.
That’s the irony of the Radiant jungle: It is easy to scout the enemies’ entry, but it is just as easy for them to scout your exit. This is the reason for the frequent ward wars in the Radiant jungle.
The Dire has different woes. Their jungle is more risky early game as rotations are more common along the river and they suffer from lack of vision into their own jungle from their T1s. Thus their T1s (and the heroes defending them) are undoubtedly easier to bring down, but if they survive the disadvantage, they will be compensated by their advantage over the Radiant’s exposed T2s.