The Cicada is a medium mech but it feel like a light when tuned properly.
The Jenner is a killing machine, no matter how you slice it but it is geared towards a specific playstyle.
The Commando is probably the easiest machine to operate for a newer pilot due to the SSRM lock ons
I have piloted all three at one point or another and can say without a doubt the Jenner is still my favorite although the Cicada was really growing on me before the final wipe before Open Beta.
Builds I recommend can be found on MechSpecs.com and they are
Commando: "
Intruder" Either build depending on your style and you are already used to the SSRMs
Jenner: "
Find 'Em and Grind 'Em" as this uses both SSRMs and Lasers (get you used to beamers)
Cicada: "
Cooler Than Garths Build" as it has speed, firepower and can still run pretty cool (but its all beamers)