I like using Travelocity to check fares and fare rules only. I then use Internet Travel Network in Advanced mode to find what flights have the fare base available and check how many seats are assigned in first to see what my chances of upgrading are. I then book my ticket on EasySabre because, with the use of shortcuts, it is faster than Travelocity. I can then send the booking to a travel agency that uses SABRE and rebates some of their commission. Also, these online reservation systems only work with 8 segments or less. If you book a ticket with more than 8 segments you need to use a travel agent or call the airline directly.