Tricky question.  I can't imagine there are many people who have done both, so you won't find many people who can really contrast the two.  Anyway, here's my two cents:

I took Trinity College's Dip TESOL.  Assessment involved the following:

• Assessed teaching practice.
  We taught a group of 12 adult learners of English, a tutor or assessor observed and assessed each lesson.
• Exams.
  Two exams.  One on language (ie. grammar, lexis, etc) and one on the teaching and learning process (ie. second language acquisition, teaching techniques and methodologies, developing a syllabus, etc).
• A presentation & interview.
  We prepared a 5min presentation on an aspect of connected speech that was followed by a 25min interview on the topic of phonology.
• Research.
  We completed 3 research projects.  For each one we had to collect and collate data through testing and observation, then write an essay outlining the rationale for the project, the process of data collection, and discuss the implications of the result.

Outside the assessed components, the course lasted 24 weeks, with just over 15 hours of training/discussion/study per week.

At times I felt like the course could've been tipped a bit more towards the practical side of things, rather than theoretical side, but on reflection, the research projects were very much "Action Research" and ensured that the course was really a good balance - you choose an area to focus on based on ideas (the theory), then set up real classroom situations in which you can test those ideas, then teach or observe other teachers and collect data to see if your ideas were right (the practice).  

From what I've heard of the DELTA, it's very similar, with a research project, exams and assessed teaching just like the Trinity Dip.  I don't know much more than that, though.

No problem, although I do hope you mean 'invaluable'.   ;)

:)  Ha ha... Yeah, I sometimes have to edit my posts more than once to get things right when my heads not all there after a busy day.  Anyway, just my insecurities catching up with me, sorry 'bout that.