For me...the old school bleep type techno of 1992-93 old jeff mills stuff....rotterdam stuff as well......when sounds were fresh....everything was so new....now everything is cookie cutter for the most part....the best direction techno had was when it had no direction....IMO
With that said...production wise....techno will always push the envelope...keeping it at the fore front of EDM over other genres that havent evolved much over the past 15 - 20 years....