I've had a Nextbase SDV17-S for about a year now, and have found it to be quite good. The only thing I'd comment is that the quality of the picture isnt the best (although it is quite good). I think my model is quite old, and they have moved on, so I expect the later models to be even better. The speaker on my player is just about loud enough for use in the car, whilst the headphones sound is brilliant. It is a very nice dvd player, especially the slot in version, but that is my preference. Mine plays SVCD, MP3 and Jpegs fine, but again, this might have improved since I bought mine, with DivX and XviD being included on some.
The best thing to do is go and have a look, if you like what you see go for it, it is of very good build quality (my daughter of 2 has been using ours, so imagine), the battery (on mine anyway) lasted 4-5 hours (Which is very good).