I'm sure a lot of people will chime in here, but a couple of things I notice...
1) Good that you are working with Buzzz, Roc, and Leopard. These are all good beginner discs that will end up teaching good form (my form is unconventional, but don't let that bother you on the advice front). The Eagle and Valk you mention are also good discs to start with. In my opinion, of course... The Valk is one of the first discs I threw, and I don't throw them anymore, but it was good for me at the beginning. The Z Buzzz will keep its flight characteristics longer than the Roc will because of the plastic, so I would suggest either getting a few of the same discs in each mold of cheaper plastic, or really work that Buzzz hard for form help.
2) If you are turning over your Leopard too much, there are a few things you can try.
First, lighter and DX plastic will flip/turnover sooner than heavier or more durable plastic. If you FELT comfy with a Leopard at one point, you can try them in Champ or Star plastic or go a little heavier. I have a Glow Champ Leopard that is pretty beat up, but it turns over in a way I want it to.. Love that disc! The "seasoning" period for better plastic is longer, so the discs will retain their flight characteristics longer than the DX or Pro plastics.
Second, if you are not doing it already, you could release the Leo with a little hyzer; that is, with your arm at an angle that is not level, with your hand closer to the ground. It doesn't have to be by much - a few degrees at most; the intent is to start the disc leaning this way -> / slightly so that it "flips up" to fly straight once it is in flight. I have a number of discs with which this is the norm.
However, my flippiest disc is a Latitude 64 Gold Line River. People swear by the River, and it GLIDES AND GLIDES when thrown right, but I turn it over way too much, which is why... Lastly, if you are turning the disc over every time, you might have what is referred to as OAT (off-axis torque). I probably do this enough, and would benefit from learning to get rid of it. That is, your wrist is rolling over during your motion and making the disc turn over faster, while it would not do so if your wrist stayed "on-axis" through your motion. You could try slowing
your motion down and making sure that it is smooth
. Don't try throwing at 100%, but more like 75-80% so that you can pay attention to each part of your form, and you may notice something.
If you have the ability to film yourself throwing, you might think about doing that and posting it here. Some of the members here are great at picking apart form through video (alas, I do not count myself among them).
Nothing beats practice, though. Keep working the kinks out, and good luck.
All you other people, feel free to chastise me for my advice to the new guy.