Well, i can only give you information of the 731 as i have one.
I bought mine about 3 years ago, i have done so much work with it over the years, it has never let me down.
The good and the bad.
The good: You can still get parts for these easily from Bobcat, Engine starting is a breeze, Uses very little fuel, Easy to maintain, the hydrostatics are basically bullet proof.
The only bad thing i can say is it has an air cooled deutz engine, it is quite loud and vibrates a bit.
With that said, the engine is VERY reliable, its just noisy.
As for the fact it has a 30 hp engine, the 30 hp is more than enough. I have never stalled mine, just run it at almost max throttle and you will be fine.
A few tips if you get the 731, for cold starting push the throttle forward about 1/4, go to the engine bay and push the button on the injector pump (this is for excess fuel). You will hear a click, jump in and turn the key. It will start very quickly and blow a bit of smoke. You only need this when its cold outside, when its warm it will start right up.
There is also a *hidden* bronze filter on these machines and if you get it, let me know and i will explain where it is located. Chances are it has never been replaced. When it gets blocked the machine squeels when you try and turn and causes a lack of drive power.
Personally i would go the bobcat, just because of the service support that is provided. If you ever have a problem you simply talk to the service section of bobcat and they will give you information without a second thought. They are happy for you to do your own repairs and they will tell you what you need to do.
From what i was told about case, they hold all their information very close to home. They don't want you to do any repairs your self. I don't know if this is true, its just what someone told me that owned a case machine.
Good luck on your purchase, either way you will be thrilled with owning a skid steer, they save alot of work!