We are launching a web site that potentially will have high traffic with users registration. Is it better to host it with a web-hosting company or its better to own some space in data centers with some (or lot of) expense?

Any advice with cost and strategy would be appreciated. If i go with web-hosting company which is fast and reliable?

There can be no question that a data center offers the more reliable and secure environment for a website project, but at what cost? Every data center website I have visited does not list their prices, and the pricing structure varied greatly from center to center. I'm guessing that data centers are not cheap. Web hosting, on the other hand is cheap ( you can get started for about $50 to $100). Outfits like Go daddy, Apollo and Yahoo hosting offer very affordable rates and are pretty much on the same level when it comes to reliability and speed. But if you break down the reasons that make a data center better than a web hosting provider, some of the advantages of the data center don't seem too important any more. Both data centers and web hosting providers offer:

-Linux and Windows based platforms.

-Redundant power backup and cooling solutions.

-Tier 1 backbone connections.

-Compatibility with complex languages such as Pearl, PHP, and Python.

Initially, if the website is expected to get a lot of traffic, there is no doubt that a web hosting service will be adequate, and it will keep the startup costs down. If a move is necessary in the future (and it may be if you get the traffic you predict), perhaps a move to a data center may be in order. (moving a website is not as difficult as it sounds. Most hosting providers offer services to assist with the move) If you actually get the traffic you want, I would seriously consider moving to a data center. They have sophisticated fire suppression systems and air conditioning units that offer the best possible up time you can expect. They even incorporate a raised flooring system that negates the risk of static electricity. Even a good web hosting provider will not guarantee %100 up time.

Hope this helps.

A web-hosting company will be cheaper, but a few new blade servers from intel will work like magic.

You asked it twice, so I'll answer it again! - Another option is chrooted hosting on servers with good domain-to-server ratios. You get the usability of "standard" hosting with enterprise reliability, access and security. Google link below with some more info.