I went through this over the past year and advise going in this order:
- ask around to friends to see if anyone is looking to buy into Vintage or Legacy; if so, sell direct to them for ~TCG low-mid prices.
- Post your stuff on the High End MTG group on Facebook (
https://www.facebook.com/groups/highendmtg/). Gets a lot of traffic and people rarely get screwed there.
- Sell your stuff on MTG Salvation.
- Try and trade your smaller stuff in batches up to bigger things that are easier to move (duals, power). Do this in person and/or through the various online trading venues out there -- MTG Salvation, etc.*
- eBay.
- Sell to a dealer.
*What's that site that lets you trade cards for a trading-only currency which you can use to facilitate other trades on the site? I forget. Its home page has an animation of trades happening around the globe.