The BM rating will undoubtedly give you the most "excitement" and "adventure", over the ET rating. You could be doing many different types of work: Law Enforcement, Search And Rescue, supervising non-rated personnel, facility/vessel maintenance (painting, lawn mowing, snow plowing). It is a physical and very well-rounded rating, giving you a wide variety of work opportunities.
The ET rating is a very technical job, which is great if you're interested in the electronics field. Just understand that, on average, 90% of the time you will be stationed on cutters that deploy for months at a time (as compared to 50% as a BM), and your job will not provide much "action". If you enjoy sitting in a climate-controlled area, and working on computers all day, then give it a try. It's definitely a good way to get fat quickly.
The main issue is not to choose between these rates according to the A-school wait or a signing bonus. I know that at this point those are tempting factors, but even if you only stay in the CG for one tour, you need to enjoy your job. The only time I would advocate using these factors in your decision making, is if you were trying to choose between two or more similar ratings that you were interested in: SK & YN, BM & MK, AET & AMT, ET & IT...
Hope this helps. Feel free to email any questions...
I was in the Coast Guard for over 6 years. I "struck" the Yeoman rating, and then 2 years later, "struck" the Boatswain's Mate rating.