This is the deal.
The mobile DivX player is free and does a pretty good job but you are going to need to do a lot of re-encoding. The mobile DivX player caps out at support for 320 x 240 video. Pretty much anything you download is going to need re-encoding.
There is also one other facet of the DivX mobile player that always annoyed me. When you fast forward and rewind it does not show the video. There is a scroll bar that displays the time and you must judge by that.
On the other side of the coin is the Core media player.
Core player does not suffer from either one of the shortcomings I explained above. It is not limited in resolution and you can see what is going on when you fast forward and rewind.
The Core player also has a built in YouTube viewer. If you opt for the mobile DivX player then you will need an additional app for youtube. I would suggest EmTube for that.
Now here is an observation that somehow fits into all this.
I used the mobile DivX player for a number of years and on many different devices. Because I had to re-encode everything for it I never once experienced poor quality playback. I had ultimate control over the playback because I had to spend the time converting video's and compiling a mini duplicate collection to my video collection.
I have been using the Core player for only about 2 months and only on my
N95-4. I no longer re-encode video. I just download stuff and move it to my
N95. Since I am no longer controlling the bitrates and resolutions I have encountered stuff that does not play back well. Sometimes files just have 'to much' to them and Core will stutter and glitch.
Best of luck,
dumwaldo