Which bike should i buy?

When you talk about quality and value, neither of these bikes will offer you much. Although initial price will be higher in a bike shop, long term cost will be lower. I was in my local shop recently, there was a person there who had just bought a bike in Canadian tire, it still had the stickers and tags on it. The bike was brought in for a complete tune up because the brakes and gears didn't work properly, it hadn't been assembled correctly. Bikes like those go out of adjustment quickly, requiring frequent maintenance. Bikes from department stores only come in one size that probably won't fit you. 24" wheels are for children, not adults. If you have short legs for your height, you need to be properly fitted on a bike, Sears or Canadian tire are not able to do that for you, they don't have bikes in different frame sizes.