Would appriciate some insight from traders of these spreads. Is there any reason to build a spread out of puts? They are relatively expensive OTM and ITM (the part you buy) so you should always prefer Calls, right? (maybe unless you are a bit bullish and feel it would be easier to adjust with Puts)
Yes there are reasons. It would depend on your strategy, outlook for the security and liquidity of the options. Lower priced options are typically more liquid with tighter spreads. Also, the puts will have a different skew than the calls and will trade differently as the security goes up and down.
The synthetic with the better fill is the better choice. If neither is prevails, the one that might have more contracts expire worthless would be the choice since that involves less exit slippage and commissions. Why do you think calls are cheaper than puts?
In equity/ETFs, calls are normally skewed down as you move up in strikes, while puts are normally skewed up as you move down in strikes. So, the 25D Put will be more expensive than the 25D call, most of the time.
Sorry, what is the D for in 25D? Maybe I'm not following something. Yep, OTM options are skewed but how does that relate to doing synthetics? If I'm bullish, I'm going to play with the puts not the calls. And if spreads are involved, I suspect that the skewing is fairly irrelevant because what you might overpay on one leg, you're overpaid on another - somewhat of a wash.