From my personal experience, 1v1 Fighting and 1v1 RTS were the most challenging game genres. 

When it comes to what's more enjoyable between them, personally fighting games were only enjoyable if the game was well-designed at the level like Guilty Gear Strive, DBFZ, etc.

As for RTS, even if poorly made, the presence of numerous units and buildings in any RTS inherently lends some weight to the gameplay, plus the compexity nature of RTS, making it somewhat enjoyable even if the game design gene