I really like International Express Elementary. I haven't seen the other International Express books, but this is really enjoyable to use, has a good focus on skills such as telephoning, and emailing, and deals with grammar very well. The workbook is also excellent, giving plenty of practice to students. I haven't seen the teacher's guide.
Market Leader assumes that the students are high-flying business people, or people with an academic interest in business, which is great for certain groups of students, but for office workers who don't have a business degree/aren't interested in high finance, cashflow, brand management etc. then I would recommend International Express.
In a related matter I put a question on the Market Leader discussion forum (http://forums.longman.com/DB_Topics.aspx?fid=8
) back in October and there has been no response from Longman. I can't believe that they have nobody moderating/monitoring the discussion forums.
Finally, I have the teacher's guide for Market Leader Upper Intermediate and think that it is very good (despite a few errors). There are lots of newspaper articles at the back, complete with exercises. Perfect for homework, broadening vocabulary etc.