I was in the same boat as you. The things that won me over to the SanDisk e250 was the price ($169 at BB) and the features. It is a great product and in my opinion better than the iPod nano. The most notable feature, IMO, is the video playback. While it isn't stellar, it is suitable for the occasional music video. The scroll wheel makes navagation very easy, however not as easy as the clickwheel. It doesn't scratch as easy, but I have gotten some minor scratches, but nothing noticeable. I love the ability to expand via the MicroSD slot. While it is bigger than the nano, it is by no means big. Longer battery life and bigger screen make up for the extra thickness.
The Samsung YP-Z5 didn't suit me. It didn't have any extras like FM tuner, video playback, extra. I wasn't fond of the controls either. It is very hard to first use it, but you do get the hang of it. The one thing I don't like about the controls is that is all one speed which makes it harder to narrow in a choice.
My old mp3 players headphone jack broke so I need to replace it and I have been looking up flash players for about a month and I have narrowed it down to the ipod nano, Samsung YEPP YP-Z5, SanDisk Sansa e250. I like the SanDisk because of it's features but I like Apple's and Samsung's look better. But the Nano scratches easily and I am not for sure the Samsung has the enough features as the other two.I just want to here some of your experiences with these players.