go for the biggest engine you can afford ;-) ... it will make the job more
relaxing. for the size of lawn you mention i'd reckon that a 19" cut is
about right: after this size, prices jump alarmingly for not much in the
way of less work to do. my advice would also be to buy a hayter machine (if
you can get one where you live). they're slightly more expensive than most,
possibly cheaper than a honda, but by god they're well made. whatever you
do, don't try and save a few quid at the outset - you'll regret it later!