I've tried several scanners, including a flatbed scanner with a TMA (Transparent Materials Adapter) for slides, and none of them can even come close to my Nikon CoolScan 5000. It's much brighter than any other scanner and has an infrared channel for reducing noise.
I also highly recommend VueScan as the scanning application.
http://www.hamrick.com/ It blows the Nikon software to pieces.
I have the 50 slide batch tray for the Nikon and it works great. My recommendation for a workflow is to batch scan a whole bunch of slides using the batch tray and save them in RAW DNG format, that way you can walk away while the 50 are being scanned, then post process the files for color, etc. on your own time without waiting for each slide to be scanned before editing.