For simplicity you can't beat Serena Williams' serve. It's very clean.
And it has serious power:
"She translates all that into intimidating power. Williams’s average speed on her first serve against Kvitova was 109 m.p.h. David Ferrer, a Spaniard who is into the men’s quarterfinals, has been averaging 109 m.p.h. on his first serves, too.
Williams’s average speed on her second serve Tuesday was 92, faster than the tournament averages for two men’s quarterfinalists: Florian Mayer (87 m.p.h.) and Andy Murray at (8
The challenge of trying to "copy" someone else's serve is that they often incorporate elements unique to the individual. I suggest focusing on the fundamentals of a good serve and practice it frequently. If you try to copy someone's serve that includes unique "hitches" you might be making things more complicated for yourself.
And practice is key here. I chuckle to myself when I hear fellow rec players say they're "working on their serve" while playing a casual match. No, they're serving during a casual match, nothing more. To work on your serve you need to hit a lot of balls over many sessions over many weeks and months and years. Since it's often a pressure shot you need to work not only on its physical aspects but also its mental aspects
You need to practice and develop your ability to focus purely on the ball as it floats above your head and you confidently swing to contact, trusting that your smooth, relaxed stroke will accurately and consistently send the ball to your intended target point with pace and spin.
Too often players, especially male players, focus on power alone forgetting that CONSISTENT and ACCURATE power comes from relaxing and focusing and not swinging like a mad man.
I think that we rec players make tennis much harder than it needs to be by putting the cart before the horse. We worry too much about stroke mechanics before taking care of the many factors that make a solid stroke so much easier. And whether its a ground stroke, volley, or serve, the first step to any solid stroke is the mental part. You need to learn how to be relaxed physically and intensely focused mentally.
After that any stroke is so much easier.