I can relate very well to your situation (Yammie GH1).
(I also used quarters but only to lighten the touch of my piano temporarily to see if it changed the weight - it did.)
would you suggest that i practice mostly on mine (build up strength, endurance) or that i practice the ones at school (increase rapidity and fluidity)?
Liszt practiced on the heaviest touch he could find and performed on one with a light touch. Chopin detested this and said the touch must be very light.
Playing on a heavy touch requires an increase in isometric stength so that your fingers will not buckle under the load. (Isometric strength is not the same as grip strength.)
Playing on a heavy touch requires a different technique to overcome the resistance. Unfortunately, this isn't very helpful when playing on a light touch keyboard which requires a different technique. You may notice that in loud and fast pasages you press down more with your arm on a heavy touch but this same technique on a light touch results in "i have a tendency to play a little louder." Playing at the same dynamic level on a light touch would allow you to use much more wrist action - a difficult technique to learn on a heavy touch piano (and I would say it is impossible to learn on one). Example gratis: the fast octave passages in Lizst's Hung-Rapper 6 fatigues me after a minute. I am using much forearm movement to press the keys down. On a light touch piano I alter my technique and use a lot of wrist movement which is impossible on my piano because the keys won't be depress far enough to have consistent tone. I also play these passages much faster on the light touch pianos.
Here's an example of physics about mass and the required force to put an object in motion. Which is easier to throw: a baseball or a bowling ball? Clearly it is the baseball. The bowling ball is too heavy. You may even injure yourself trying to throw the bowling ball (which was meant to be rolled across a laminated floor).
Chopin said that the body must be supple. Tension does not lead to suppleness. Tension inhibits suppleness which inhibits playing well which inhibits good music making. And Liszt? The way he practiced required a lot of strength. He practiced until his fingers could not play another note because they were so fatigued and that was when practice was over for the day.
Strength does not matter unless you have a heavy touch piano. Endurance does not matter, either. If you can practice and play for 2 hours you have all the endurance you need unless you are preparing for a 24 hour marathon piano competition but these do not exist (but prove me wrong, and if it does...
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Chopin also said that one must practice only on the finest instruments (Pleyel with a light touch and excellent tone). How many of us can afford a 9ft Pleyel? And then fit it in our homes? And then not have the tremendous sound deafen our ears? But I do agree that one should practice on only the finest instruments but it just isn't practical.
Topic: Piano action and technique