Since registration of new domains has become incredibly fast these days, with the online scripts provided by registrars and resellers, within a few seconds your name will be registered and then you will be the owner. It's not like doing some paper work and waiting for days or weeks before registrations fully take place, so the option of first come, first served can be applied in most new domain registration cases.
If you really like an address, and find it available, do not hesitate, especially if your hosting account has credit or funds or you are in a position to have it registered. Do not postpone it, especially if it contains some top business names because who knows, maybe a in a few days it will be gone and registered by one of your competitors or someone who parks domains and sells them at higher prices.