The plusses of OTP are that you get to choose the unit you want in the building (if you're an early buyer), you may have limited scope to customise it and you do lock the price in. If it's going to be a long term PPOR then capital gain may not be so important to you, though it's a factor if you want to use equity to finance IP down the line.
My experience has been unfailingly poor. Two Central Equity apartments in Melbourne CBD bought OTP in 2000 and 2003 (I lived in the UK at the time so was subject to FIRB), each sold after seven years, lucky to get my money back (significant holding costs in the meantime) and my home now (449 units x 43 storeys) bought new when just completed in 2007 would now sell for just a little more than I paid - some in our building have resold twice with the price dropping along the way. When I bought the developer rebated half the stamp duty - done this way, I guess, to keep the higher price on the official record.
IMO key factors for OTP poor performance include overseas OTP buyers only being able to sell to Aussie buyers and people only realising the effect of OC levies after completion - I pay around $8K, would be around 20% of the rent if I was letting. The legal position has changed somewhat since 2005/6 but our developer locked our OC into highly unfavourable contracts, probably getting kickbacks in return. Most of these have been unwound, but at great expense and only because certain OC committee members have put thousands of hours into pursuing this.
Ultimately it's your call: going OTP is a gamble, but so is waiting and buying down the line. But if you were to rent in the building with a view to buying after a year or two, you'd then know exactly what you were getting in terms of building quality, management, OC levies etc.