I haven't seen some seasons in so long, I couldn't remember anything about episodes and Legs even if I read Wikipedia summaries. lol Also, there are well designed Legs that produce duds as episodes and poorly designed Legs that somehow make great TV.
So from the seasons that I can remember (and some I probably know by heart! hehe)
TAR3
Pretty much every Leg, but...
Both Vietnam Legs (Legs 11 & 12) - Obviously just epic and all-time classic episodes and Legs.
TAR4
Malaysia (Leg 9) - A simple, straightforward Leg that turned into a grueling, dramatic Race.
TAR5
The Philippine Legs are memorable episodes thanks to the teams, though the Legs themselves maybe don't hold up as well aside from "My Ox is Broken" Otherwise,
Uruguay (Leg 1) - Now this is a season premiere. A great first Leg with solid tasks and tricky clues. Add in the teams all delivering, and you've got a great one.
Argentina 1 (Leg 2) - Maybe since I recently just watched it again, it's fresh in my mind, but it was a hectic Leg with lots of drama and good competition. Again, the teams helped make the Leg much more than it was on paper.
TAR6
Another season with a lot of great Legs. But I'd go with:
Ethiopia (Leg 8) - Great Leg with both physical tasks and some attention to detail and luck. Plus donkeys!
TAR7
India SuperLeg (Leg 8) - TAR7 is pretty low on my list. But Gretchen on the elephant is enough to make me choose it.
South Africa (Leg 5) and Botswana (Leg 6) are close as well for Gretchen's fall in the tunnel in South Africa and the epic finish in Botswana
TAR8
Panama (Leg 5) and Costa Rica (Leg 6 and half of 7) are in a league of their own for this season, obviously. And I'm one of the very few who actually likes (loves?) the season.
But for the stateside Legs, I'd go with:
New Jersey/Pennsylvania (Leg 1) - Mama Weaver almost getting killed by a buggy and the little kid of the Black Family getting stuck in a ditch is epic stuff.
But most of all, the Finale SuperLeg was pretty excellent.
TAR9
Oman (Leg 7) - Great Leg, horrible result.
TAR10
Still the most grueling and physically challenging season ever.
Vietnam 2 (Leg 4) - A great, full Leg
Madagascar (Leg 8) - Mainly for the excellently edited sequence featuring the Intersection. 2 teams at the Fast Forward while the other four doing the mattress Detour. It was pure insanity and amazing. Those 5 minutes are more exciting many entire episodes in the HD Era.
TAR11
Not really sure, even though I love the season.
Hong Kong (Leg 10) - Very cool, unique tasks.
I would choose Tanzania (Leg 6), but the invisible storm keeps me from doing so lol
TAR12
Another hard one.
Burkina Faso 1 (Leg 3) - A fun, full Leg even in such a small area and with only a Detour and Road Block
Honorable mentions to Netherlands (Leg 2) and India (Leg 8)
TAR13
Brazil 1 (Leg 1) - Also recently watched and it was another great premiere. Very full opening Leg.
Honorable mentions to Bolivia (Leg 3), India 2 (Leg 7), Kazakhstan (Leg 8)
TAR14
China SuperLeg (Leg 10) - Basically two Legs of great tasks.
TAR17
Ghana 1 (Leg 2) - Perfect kind of Leg for the early part of the Race with 10 teams.
Russia 1 (Leg 6) - Really one of the best Russia Legs of any TAR. Just great tasks on a well-designed Leg with teams delivering.
TAR20
Paraguay (Leg 3) - Challenging, unique tasks on a perfect early Race Leg. Would not work later with less teams.
India 2 (Leg 10) - Another challenging Leg with good tasks that together made a full Leg
TAR21
Bangladesh 2 (Leg 5) - Talk about a challenging Leg, this was definitely one of those. Physically and even mentally challenging
TAR23
Norway (Leg 4) - Love the Midnight Sun Leg.
Indonesia (Leg 9) - A full Leg highlighted by the Road Block
TAR24
Sri Lanka 1 and 2 (Legs 5 and 6) - On this otherwise garbage season, I think both Legs were pretty good. The Detour of Leg 5 was great. And the gasoline Road Block of Leg 6 is a perfect example of how to design Legs to allow for as many teams as possible at a task for maximum chaos.
TAR25
Morocco 1 (Leg 5) - No question. Robbed of the Emmy, it is simply one of the best Legs of the HD Era.
Philippines 2 (Leg 11) - A little biased of a choice lol, but it was a great urban Leg.
TAR26
Peru 1 (Leg 10) - A great, physical Leg that would've really been outstanding with a few more teams.
TAR27
India 2 (Leg 10) - Love the night Leg. Only a Road Block and Detour, but still a full, challenging Leg.
TAR28
Indonesia 1 and 2 (Legs 9 and 10) - Best, most full Legs of the season. But maybe pales in comparison to other seasons.
TAR29
Vietnam 2 (Leg 10) - Absolutely the best Leg since TAR25's Morocco Leg. Again, might have been even more amazing earlier in the Race.