What's a better marketing strategy: big-bang or ramp-up?

I would honestly ask yourself how buzz worthy your product is.

99 out of 100 startups and business domains wouldn't be of interest to TechCrunch, Digg, Twitter, Mainstream Media, even if you arrive out of nowhere with a great product.

Even moderately successful blogs and specialist media would want some combination of amazing product + interesting backstory + brilliant execution + customer traction before writing about you.

Thus, stealth mode could end up being a wasted opportunity when you could really be interacting with your communities and trying to fire up real grass-roots word of mouth marketing.

In addition to Jasons point re finances.... Slow burn also allows you to tailor and feedback into your marketing and PR efforts as you learn what works and what captures attention. Don't burn your yearly marketing budget on a product launch that may dissapoint!

How much money do you want to spend?

As you say, a single bang dissipates fast; usually that's not enough to get critical mass. If you're not building on the shoulders of happy customers, you have to force your message into people's eyeballs, and that means money.

Growing slow and strong can be done without money, but can take years longer. Depending on market conditions, that might be OK or it might be fatal.

Neither of these ways is "better" in an absolute sense.

Benjamin's points are good ones along with other comments above. Some thoughts:

Don't believe your own hype

Most of us "eat our own dog food" as the cliche goes a bit too much and think because we believe our product is wonderful and incredible and magical that everyone else (media, businesses, consumers) will feel the same way. Often doesn't happen that way. Having proofpoints (especially happy customers, case studies, success stories) is a key element of getting people to think it's wonderful, incredible and the rest. Plus often it takes time to get the product "closer to right" than when you launch. Real customers, real feedback, real product enhancements. That will ultimately help a lot.

The product big bang

A huge part of the answer is your product and the potential it has to create the big bang with no marketing. That is true for a lot of the big web properties. Some seemingly explode like Twitter but it was because it delivered a service that nobody else did. It wasn't because they spent a bunch of money on marketing, the product caused the 'big bang'. Likewise with YouTube. Even though there was already online video there was something that they offered that the others didn't which caused it to explode. It hit a spot of need, even in spite of competitors out there, and exploded quickly.

Cost of customer acquisition

Ultimately that's what it's all about. How much does it cost to acquire a customer via SEM, ad banners, partnerships, affiliate marketing, PR, however you market the product? Then how much can each of those scale? So SEM may be my lowest cost per customer acquisition (hah) but it may not be able to get the scale in numbers you want.

And to the point of fast vs. slow, typically with new ventures it's going to take time until you really know the acquisition costs. And those should improve over time as you tune your marketing messages to improve the traffic they drive, strengthen your credibility which helps effectiveness of your efforts, tune your site to improve conversions, tune your tactics to improve your overall acquisition costs. At the same time you have to be opportunistic.

All the best,