This is one of those discussions where you need to start with the plan for your show.
Hands down, the express is a better device. In addition the light curves allow you to mix different brands and types of lights and set the curves so that they still match as they dim together.
However, if you need 4 or 8 channels over here and 4 or 8 channels over there, there is just no easy way to get there with an express without a bunch of extension cords, or a half used express... Of course there is always the option of adding more lights
The freestyle on the the other hand caters directly to this type of need. It is also convieneint if you are doing 4 channel trees (RGBW) and want to have a single power and single control cord for each to make setup easy.
In the end though, I think the smart strings are going to make everything else obsolete except for the larger bulbs (C7, C9), which we don't have an equivalent for... yet. In a side by side, bulb to LED comparison, the SS appear to be brighter than the mini-lights I used last year...
RM