Why shouldn't ubuntu be first choice for experienced Linux users?
I'm running Linux for about 9 years, and since 2 years it's ubuntu (well: xubuntu) - I didn't try out LFS but I compiled KDE from source on a 233 Mhz PC (two and a half day, if I remember correctly) and often compiled my kernel myself.
I would call myself an experienced GNU/Linux user, and why should I avoid a userfriendly package-management, and short update-cycles?
@sarahnade: If you like to know, why your friend thinks, ubuntu isn't a linux, ask him, not us.
Differences between distos are mainly found in the installation process and there is a handful of installation/update routines, namely: rpm, yast, deb, ...(more?).
LFS is different*, and of course some realtime linuxes or such for very special purpose.
(*Linux from scratch. You get every program from source, including kernel, compiler, basic libraries and compile anything from scratch.
Since you need a compiler to compile the compiler, and a kernel, to run the compiler, and librarie used to compile the compiler, you compile some things twice or three times).
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