These machines are very different
The MBA is much smaller and much better built, but it is more expensive and has a slower CPU.
However unless you do video encoding or other CPU intensive task the MBA with SSD in operation is much quicker to open programs and general operation is much faster than a standard 5k / 7k RPM HDD.
I bought the MBA because i love OS X. It is a much better OS and the hardware is a joy to work on day in day out. Lovely keyboard, trackpad, lightweight, quiet, portable, fast, SSD, nice screen, excellent battery life. All the things that matter. But you pay extra.
You need to ask yourself, what is the primary purpose for this machine. General use MBA, editing videos or similar - MBP or HP which is cheaper.