Well, it all boils down to a few things. If you're planning on teaching English as a lifelong career, a CELTA is an OK option that can be built on with experience and higher qualifications. But, the CELTA isn't that amazing; most teachers with 2-3 years under their belt would have outgrown the CELTA already. I always see people talking about the CELTA like it's the Holy Grail.
I have been living in Asia for over 10 years and have a couple relatively successful language training centers in Beijing operating since 2007. I'd much rather recruit a teacher with a TEFL and 1-2 years real experience, than hire a fresh out CELTA grad. It's not too difficult to find TEFL courses online for under $300 (I recommend my teachers take a course at mytefl.net because they give us an institutional discount, and my newer teachers generally perform much better after completing it), whereas the CELTA is easily $1600+ and a much longer time commitment.
From a practical viewpoint? Get a TEFL, and go get some real world experience (plenty of schools are willing to take you on and train you at lower wages intern style; you'll still live fine in Asia). You'll save a ton upfront, be earning a salary within a few months, getting actual experience that counts for much more, and will beat the 'CELTA' curve within 1-2 years if you stick with it. Also, many people are NOT cut out to be teachers and may dislike it very quickly. There goes your $1600 + 9 months work. With a TEFL, you've less to lose if it turns out teaching is not your cup of tea.