If you take business, you will probably find most of the softwares that you need to run are for Windows OS. So if you want to buy an MBA and run Win OS using bootcamp, by all means. But your budget will not get you a MBA

For "smoothness" in multi-tasking, put in more RAM (normally can upgrade aftermarket, usually won't void hardware warranty, 4G stick ~ RM90), but more importantly, opt for (or change HDD to) full SSD (solid state drive). SSD 128G ~ RM300+/-, 256G ~ RM600+/-.
Asus
K46CB-WX060H, i5-3337U + Nvidia GT740M@RM2199[2kg], 2GB, 750GB, W8, 4-cell, ODLenovo
Z400, i5-3230M + Nvidia GT740M@RM2099, 4GB, 1TB, W8; 2 years warrantyS400, i5-3317U + Intel HD4000 + 24GB mSATA + 500GB(5400rpm)@RM1999[1.8kg], 4GB, W7HB; AMD HD7450M/W8@RM2199
Sony
SVF14218SG, i5 3317U, 4GB RAM, GT 740M 1GB GDDR3, 500GB HDD, W8, 1366x768, RM2399
Prices are RSP, negotiable.
After the RAM and SSD upgrade, still within your budget.
how come lenovo z400 is cheaper than asus k46c and way higher spec... something fishy about lenovo? how well is the quality?