I say Muay Thai, as someone who trained for a long time in both Muay Thai and Shotokan Karate (which I actually loved, but Karate has not evolved, so it’s a dying art).
However, I want to clear up this idea about needing a “live resisting partner.” It’s not 100% true. The purpose of forms in traditional martial arts is to train the automatic response when under pressure. Your automatic responses are trained when you’re NOT under pressure and the fight or flight instinct isn’t being fully engaged. When the fight or flight instinct is engaged, you execute the automatic response rather than learning.
For example, a basic drill we did in karate was that the instructor would yell, or use something to make a loud crack sound and we were supposed to immediately hop into our fighting stance. We’d drill this for quite some time. Eventually, anytime I heard a loud noise, I’d immediately shift into a fighting mindset and fighting stance.
There was an incident with my roommate at the time, who had a penchant of jumping out of the dark and trying to scare me when I got home. He stopped doing that after I instinctively knocked him out.
When you do nothing but hard sparring all the time, your mind isn’t in training mode, it’s in survival mode and you’re not actually learning skills. The proper way to do train is the same way you train anything. You start slow, then build up in speed and power.
Slow is smooth and smooth is strong. You work the fundamentals for a very long time and when you move to anything advanced, it’s easy. I started training kali a few weeks ago and because those movements are very similar to kendo, I’m picking it up very easy.
Do the martial art that clicks with you.