I like my Concept 2 rower. They can be found used, in good condition, and that's how I got mine.
But the best exercise is the one you will actually do.
But, you did ask for focus.
So, you need strength. I have just started fooling around with kettlebells.
The basic kettlebell move is a half squat where you swing the thing up on the way up.
That is a similar motion to pedalling. I have a 5 and a 10, and hope to get a few more
before Spring.
Another option is single leg strengthening exercises like the Step Up, Lunge and Bulgarian Split Squat
I like deadlifts, but form is crucial if you want to avoid injury. Very good for the hams and backside.
However... what ya need is an actual training schedule, a periodised schedule designed for you.