A sit and ride mower is absolutely the best for flattening out a field like area - over time, it'll be good enough to practice golf on. However, if you really want an electric solution, all I can tell you are the advantages and disadvantages for each method.
Cylinder mowers with a small roller on the back won't 'flatten' out bumpy areas, the roller's not heavy enough, and it also won't cut well if you've left the grass for too long - it leaves any extra long growths uncut, just flattens them as you go over them. It will, though, produce a stiped effect by mowing in strips, one up and one down. A hover mower will cut anything and everything, including wet and fairly long, but it tends to leave slightly 'chewed' ends to each blade of grass rather than the clean cut you get with a cylinder (though this is not obvious without a magnifying glass), and obviously, no stripes.
Regarding rollers, these are meant to firm the surface of an already smooth lawn, they are not meant to iron out bumpy areas - this kind of use usually makes things worse by depressing the hollows even further. They are also not intended for frequent and regular use on established home lawns, rather, they are used in early spring to reconsolidate any turf which has been lifted by frost. You can do the same thing with a cylinder mower with a roller on the back - you set the blades high and go round with the roller in contact with the turf, if it is necessary. Frequent use of a separate, heavy roller will also result in compaction, which you don't want if you require a good lawn.
All in all, you should choose an electric cylinder if you really want a striped effect, but to avoid washboarding, change the direction of cut each time you mow, so one time straight up and down, the next from side to side. If possible, I suggest you buy both a hover and a cylinder - you can't beat a hover when the grass is long and damp. If you have lots of bumps and hollows, you will need to do some work to address this problem by either filling in and seeding the hollows, or peeling back the turf on bumps, removing some soil, and replacing the turf.