I'd say 1.30.4. The issue with older versions is that you miss out on new content made with newer ones.
What kind of bugs have you encountered with 1.35? Most of them appear when trying to play older version maps, mostly because of texture name and location swapping they did between patches especially since the CASC replacement of .MPQ files. I mean, these are essentially fixable although the biggest issue lies with custom models that use the game's previous texture name and paths. Custom models that have their own textures and don't use any from the game's directories, don't have this problem.
Legends of Arkain crashes after playing for x amount of time (sometimes after 15 minutes, sometimes after an hour). Some custom campaigns (older ones) are straight up unplayable. Wanderers of Sorceria is an exceptionally weird one, it works fine on 1.31.1, but on Reforged, the first map I open works, then if I try to go back to the menu, or go to the next mission, the game crashes.
Some custom campaigns tend to make the game crash on 1.35. For the case of Arkain Series, Shar Dundred (author) really recommended 1.29.2 if you want to play the campaign without errors.
You can only play 1.31.1. if your campaign only support that version such as OutsiderXE's (notably Lord of the Clans), Malfurion's Quest, Chasing the Dawn, and even the most recent campaign made by Footman16, Lordaeron's Destiny. But, as you might know, this version has 2 known bugs:
1.You can't continue the progress of campaign if you attempt to load your previous saves because unit-related triggers were broken, which alter the whole gameplay (some important quests were incomplete).
2.If you exit the scorescreen upon completion of the single chapters, the game will lock up with a black screen issue.
Also, talking about the Warcraft 3 version issue, the official system requirements has been changed starting when Blizzard released a 1.27 patch in 2016, which is another big problem for those who want this legendary game in addition to well-known bugs.
1.Windows 98 Second Edition and Windows 2000 support was dropped in 1.27 (the game now requires the D3D9 and Visual C++ 2013 Runtime).
2.Windows XP and Windows Vista support was dropped in 1.30.0 (this was undocumented).
3.Rushing to 1.30+ will now cause the game to use a higher memory usage. This was obvious because the game file system has been changed (CASC).
4.1.31.1 no longer supports 32-bit Mac, software TnL, and targets D3D11 (though you can still revert it back to D3D9).
Not all versions of Warcraft 3 are free from system requirements-demands or even bugs. Even 1.26 has a memory leak issues relating to triggers.
