Best exercise class / activity for quick results?

[clevername]

I'm not looking for a quick fix as such (I mean, obviously I am...) I'm just stuck in the rut of caring that I'm a bit more wobbly and round in some places than I'd like to be, but somehow not caring enough to actually do anything about it. So I'm thinking if I started to see results fairly quickly then it might help my motivation.

For context, I'm 9st but short and slight framed. I reckon if I lost about a stone and, most importantly, toned up a bit I'd be sorted.

Does anyone have any recommendations for exercise classes or activities that show results fairly quickly so I can get myself motivated?

crossfit/weightlifting

I see a PT (used to be weekly, now fortnightly), as he really works me harder than I would ever work myself. My goals now are largely just to maintain my current fitness level, but if I had more specific goals, I know he'd be all over it, and would make sure I was seeing improvements regularly.

I also do a Circuits class weekly. I do think HIIT is brilliant, and using weights (both body and free weights) is a great way of seeing progress quickly. But the thing I find the hardest (and probably most effective if I'm honest) is running. I've 'run' for about 20 years now, and am pretty crap at it - slow and crappy stamina - but I sweat buckets and my heart rate stays constantly elevated.

CrossFit