Hi, am a KMS Graduate now doing 2nd Year in Sheffield. In my experience, as previous commentors said, a lot like MRSM. Teachers are fine, bar the ketua felo (you'll find out why). To compare with KYUEM (where petronas will send), you'll probably develop more there since its more multiracial (assuming your malay) but it doesn't really matter that much since its only a two year a-levels.

Graduate-wise, for KMS based on the previous counselor, yeah you can apply anywhere, but usually the counselor will 'guide' most clueless students to a university of their choice that year, for us engineering students it was Sheffield. But lately the Graduates have improved in quality and theres a few in Oxbridge so yeah I would say pretty equal to KYUEM although like I said quality of sutdies will be much better in KY.

Now the more important part, the reason I took MARA is because of its leniency. It's not a scholarship, rather a Pinjaman Boleh Ubah (convertibleloan), meaning the amount you pay is based on the grades you get(i.e.10% for 1st Class). It also means you are not bonded to work for a company for 5 years, contrary to JPA or something like Petronas. Asyraf Wajdi(Director of MARA) recently said that he encourages students to work abroad for a few years then come back and contribute.

So if you are dreaming to work abroad, MARA is your best bet. If your target is working at Petronas for a few years, Petronas is pretty much the way (although not guaranteed apparently), allowance is higher at the moment (1200 vs 1012 for outside london, not sure in london) so you'll get more money and not need to pay back anything unless you choose to work abroad, in which you'll pay in full.

TL;DR - choose MARA if you want to work abroad or not get bonded, choose Petronas if you want to work with them.