想买个gps,哪个比较好

我下个礼拜6要去o'hare airport送人去机场还要去milwaukee看一个朋友，8月份的时候还计划去东海岸玩一圈。我出去玩一直用yahoo map, I admit sometimes it was stressful to drive and looking at the map at the same time, but it wasn't something i could not handle。但总是觉得要是有个gps的话就会更方便一些，我这些日子一直在看amazon上面的review, 重点是garmin nuvi760和nuvi680. I guess what bothers me now is some ppl wrote very positive comments, others gave 1 or 2 stars rating on the same product, so I was just a bit confused after reading the comments.
Any suggestions from any1? my price range is under $250