I decided to compare the 25 US seasons (taking out TAR8 and not counting the upcoming 27th season) and find out how unique their routes were statistically. How I decided to compute this was to take the stats on Wikipedia as to how many *seasons* (not pitstops) had filmed in each country. For instance, I took the route from TAR1, then saw how many seasons had visited each of the countries that TAR1 visited (discounting the USA in this and all seasons). For instance, South Africa got a 3, Zambia got a 1, France got 8, Tunisia got 1, Italy got 7, India got 10, Thailand got 6, and China got 11. The resultant average was 5.875, which is high comparatively. As you can see, TAR1 also has two unique countries to that season. So, below, you'll see the seasons ranked by route uniqueness (where a lower score is more unique), as well as by number of unique countries.
Disadvantages to this method: As in the case of TAR1, South Africa was only a 'get out of the airport and hop in another airplane to another country'; however, this country was still counted. Additionally, territories like French Polynesia got grouped with France, Guam with US, etc., in the style of Wikipedia.
So, this method is not perfect, and is just one way of looking at things.
Seasons by uniqueness (Season - Score)
5 - 3.363636364
15 - 3.375
19 - 3.444444444
25 - 3.5
23 - 3.75
10 - 3.833333333
7 - 3.888888889
12 - 3.888888889
11 - 4
6 - 4.1
17 - 4.111111111
3 - 4.272727273
13 - 4.428571429
22 - 4.5
2 - 4.857142857
26 - 5
9 - 5.111111111
21 - 5.25
20 - 5.333333333
24 - 5.714285714
4 - 5.75
16 - 5.75
1 - 5.875
18 - 5.875
14 - 6.625
Season by number of unique countries
Six unique countries: 10
Four: 5, 6, 12
Three: 19
Two: 1, 11, 15, 20
One: 3, 7, 9, 13, 14, 16, 17, 18, 25, 26
Zero
: 2, 4, 21, 22, 23, 24