With the Oanda demo just know that if you want to pull account history that it only pulls the previous 6 months or so. So basically if you trade for longer than that you should pull the data into excel and update it that way, otherwise your trade history is lost. However, P/L remains intact the entire time.
I have the Forex.com Metatrader4 demo on one computer. If it expired it wouldn't bother me too much but it's still working. One poster here has a point though, at one point, it's sort of better to have at least a micro lot account to practice with real money. I have a micro lot account with FX Open and can use MT4 even though it's a micro lot account. The only odd thing is doing a wire transfer just to get an account if you're in North America. You can even trade 1/10 of a micro lot. I found that out once actually by accident when I put in 0.1 in the platform and it worked. Hehe, cheap way of testing ideas.