Currently, 175 visas are being processed in 6-9 months, for the simpler cases that do not require lengthy security checks.
The advantage with waiting for a year for your employer to sponsor you is that the process is much easier and you will also not be affected by the impending rules changes. On the other hand, whilst you are on temporary visa, if at any point your employer or yourself decides that it is not working out and subsequently you end up leaving your current job, then you'll only have 30 days to either leave the country or find a new sponsor.
It all comes to down to each person but I preferred to secure my future on my own, without relying on an employer and it turned out to be a wise decision. I first moved here on a 457 visa as well and got my PR about 2 months later (I'd applied for it a few months prior) and I can only describe the time that I was on employer sponsorship as quite possibly the worse experience of my life! I was even working for a large multinational company so I certainly did not expect them to behave the way that they did.
If things are working out with your employer, then by all means, wait a year. Otherwise, apply for a visa on your own.