This topic has been discussed a lot on this forum. And I mean a lot. You could do a Search either using the search box on the Appliances Forum page, or google. In any case, I kept a thread from 2008 (!) that contained a post which just summed it up so well, and I will copy and paste here:

I think it can be summed up rather succinctly as follows:
Cleaning: Proponants of sealed burners will say that they are easier to clean, a quick wipe is all you need. Proponants of open burners will say that it's easier to clean a removable drip pan and bowl, and you have less risk of clogging up the burner during boilovers or the cleaning process itself.

Airflow: Proponants of open burners will say that the better airflow provided by open burners makes the flame more efficient. Proponants of sealed burners agree that sounds good in theory, but note that their burners work just fine.

We have yet to see a clear winner in these arguments, so I say go find yourself a range you like then memorize your talking points accordingly, so that you're prepared should someone question your decision.

Me, I have a sealed burner range. I will be getting an open burner rangetop for my next kitchen (whenever that will be). Right now, I do have to take a toothpick to the sealed burners after a spill, and scrape away at a tiny 1/16" brown ring that occurs around the burners. I believe this would not happen with open burners. Having said that, I've been cooking for my family for years on my sealed burner range, all kinds of food you name it, and never had any complaints.

Also keep in mind that the Bluestar has star-shaped burners, and that might make even more difference than open vs. sealed. When you have the typical ring burner, your flame is around the circumference of the pan, with an area in the center that will always be cooler than the circumference because there is no flame in the center. A burner in a star-shape offers flame distribution across the base of the pan, for more even cooking.

If you want a star-shaped burner that is sealed, Thermador makes it. The complaint about the Thermador burners is that on ultra-low the burners click. Some people find this annoying, others do not care and do not notice, or, they rarely use the ultra-low. If you want a star-shaped burner that is open, then the Bluestar is for you. Having said that, many who love the Bluestar burners do not like the ovens. The Bluestar ovens have been problematic for a number of people. The solution would be to get a Bluestar rangetop (i.e. not a range), and a separate wall oven or ovens from another manufacturer.

I know. Too many choices. Perhaps budget will be your decision-maker.

This post was edited by shannonplus2 on Sun, Dec 28, 14 at 20:51

Costco sells Bluestar? With 5 burners? It is interesting to see what gets sold in different countries...burner type is really personal preference. I spent my childhood cleaning up open burner drip pans and I will pick a sealed burner any day of the week. But they do require cleaning around the inside edge as shannonplus2 indicated.