My colleagues sat down with our regular air-con contractor to hammer the inverter debate when this inverter thing 1st came to the market.
1. Based on TNB rates a couple years ago, there wasn't much savings for 1HP as the installation cost is about RM150 more vs the normal. It need larger copper pipes and electrical cables to the compressor.

2. Inverter air con will save electricity when it is set between 26 - 28C. Otherwise it is the same as the non-inverter other aircon. In addition you will need to have a ceiling or wall fan running to ensure constant and better circulation of hot and cold air.
So less than 1.5HP will only justified itself, if installation cost comes down to be the same as ones without inverter and TNB tariff  increase up dramatically.

All brands these days have almost the same quality control and they use the same parts from almost same manufacturer, only casing have different labels and design 

My 2sen observations are:-
Panasonic - Quiet but sensitive especially when environment are oily & dusty. Nevertheless, however Ulu the place in Malaysia, also have service center and agents!  , Which is an important consideration in its maintenance.

York - Cheaper, robust but noisy after 5 to 6 years. Most offices and restaurants use York.

Others I don't have experience using them...but I understand Daikin are also popular in Sinkapo. 

Others,
Need to consider the height as well. A room with these dimension 10' width X 20' length X 12' height, needs a 1.5hp.
If smaller hp then the compressor will be working very hard and non-stop aka using more electric and wear out faster.

Any of your walls/windows facing the sun? Beside getting sun-out curtains for windows, you can planting trees or small leafy bamboo to shade the expose walls.
Are your ceiling well insulated? You may consider have it insulated with rock-wool. Initial cost maybe high but if this property is your own, long run it definitely pays by itself.

Nice to hear that, btw what's the HP?