It could go either way. What do you prefer? Do you like to run or walk, or do you prefer low-impact exercise, such as biking?
If you look into a bike with adjustable tension hand bars as well, like an air toner, you may be able to save yourself some money and some space in your home, by having one machine that will do both jobs. These generally have a large fan blade, in place of the front wheel, and allow for a push/pull motion with the arms, in conjunction with the pedals.
If you take your feet off the pedals, you can use the arms only, and work your chest, back, biceps and triceps, along with a bit of shoulder and obliques all at once.
If it were me, I'd go for that type of bike and skip the rowing machine. Then, you can walk or run outside on nice days, and still get a heck of a workout indoors in bad weather, or whenever you want.
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It would look something like this
http://www.bicycleseat.org/images/fitness_1.jpg