Both are well-built boats and compete quite equally across the world. For the 2005-range, the Nacra F18 has been replaced by the Nacra Infusion, and the Tiger has seen some fit-out and construction changes but the hull shape is the same. If you are intending to race in the F18 fleet, a 2005 model of either boat will be a very good entry and you're likely to get multiple sails, like a newer jib or spinnaker for example.

Check carefully for leaks (particularly in the board wells) and previous repairs, and look over your foils for signs of damage. Those two things are good indicators of how hard a boat has been used and how well it has been maintained. Expect to do some rigging replacement.

Prices for a two or three year old boat have been very low for some time, but with prices for new boats and sails taking a bit of a jump in 2008, you might find the price for a used boat is going up as well and there may be fewer boats on the market.

Good hunting - keep us posted on what you find.