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, OD
Lenovo
Z400, i5-3230M + Nvidia GT740M@RM2099, 4GB, 1TB, W8; 2 years warranty
S400, 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.
Are you selling those model? And Macbook is not necesary? sorry i am quite dumb in this kinda techno thing.
The price you stated there included all? Like for Lenova Z400, RM2099 included Nvidia, 4gb, 1tb and all that?