First I would think you have to answer the question - What about 'mobility' do you like?
As in the entire package? Then Laptop is your option.
If a Screen/Monitor is no probem 'Mobile' but @ a location AND
you want a bit more horsepower than a laptop provides,
Then Gene Build is the way to go. The Z77's are hot, hot, hot.
The AMD PileDrive is very promising hoped sometime in the near future.
As to models G..15"/17"approx-G55/G75- The rest is to as you like.
Ram,Blue-Ray/Dvd,Ssd/Hd ... ect. ???
Older models? Answers its own question. New, Improved. In my way
of thinking. I buy the best available tech at the time I am going to make
the purchase knowing it is obsolete in mere months. Generational
improvements move forward and ongoing updates are usually for
the most recent models..also to be considered.
The advantage in my view of the G53/G74 is we know all the models
that are available and any known issues. The G55/G75 are hoped
to be the update to all of them.
Building a desktop today has very little limit as to power limits
you can reach .. depending on your pocket depth.
The G Series ranges from $1000.US refurb lesser versions to
about $2500.US for top shelf before Modd'rs and Tweak'rs take over.
(*Make sure the screen is 1920x1080 if thats what you expect.)
Desktops ... Depend on How Much?
Cpu Power, Ram Power, SSD's, Quad/Dual GPU's, Sli/CrossFire .. Monitors/Screens..
How much of what? What will you be doing with it. Multiple Monitors/Projectors
WideScreens? Gaming,OverClocking,AnyThing You can dream Up? What? How Much?
You can build either the CrossHair V AMD / Sabertooth ect .. Or ..
a Endless array of possibilities on the Intel side both starting @ about $1200.US
before Screens/Monitors and other goodies.. expect about $5000.US+ and
up for top shelf ..and up..ok, way up, if you like and can.
Laptop/Mobile - Gene/Portable - Desktop/Powerful ... I think.
Welcome to ROG.c.