The only super-detailed aircraft which comes in the free version is the TF-51, the unarmed P-51 trainer. The Su-25T is near the top of the middle-depth flight sims, where you have to learn a lot of keystrokes without the benefit of actual switches.
If you're looking for the greatest amount of switch-throwing and the widest array of procedures, the A-10C is probably your bird. Otherwise, just go for one of the in-depth aircraft (everything except the A-10A, Su-25 and Su-25T, Su-27/33, MiG-29, and F-15) which strikes your fancy. Or, if you like the idea generally but aren't entirely sold on military aircraft, you can find similarly full-fidelity civilian aircraft for FSX and/or Prepar3d, from third-party vendors.