Cost will be one of the biggest, if the not the biggest, factor. I don't know the market price for a Marineland 300DD, but a quick Google shows ~$1900-$2000. I can imagine Coast to Coast for a similar tank being $3000+. My 75g from C2C was about $1000, and that's with a sale they were running on their 1/2" Starphire glass.
However, if you want a customized - glass thickness, rim or rimless, external overflows, etc., a custom tank will get everything down to your specs.
As for longevity, I can't comment. My C2C tank is 4 years old and running like it was day 1. /knock on wood