Quote from MTE:
There is no hard rule on this as it really depends on the situation (i.e. a lot of factors can come into play here). Anyhow, the mid in your example is 12.65, so if I wanna buy then I would initially try @ 12.70. If that doesn't work then, assuming I'm ok with paying more, I would try at 12.80. Similarly on the sell side, initially try at 12.60...and then possibly at 12.50.
In addition, it is usually easier to get filled on a spread (vertical, condor, etc) close to the mid point, just because the spread is already a partially hedged position so a market maker may be more willing to trade it than an outright call/put.
I've found on the example of 12.40 - 12.90 that I can usually get filled at 12.75, but not nearly as often at 12.70. Also, like you said, spreads seem to get better fills with less effort. Although I have found it difficult to get mid fills trading SPY options. Not sure why though, cause the volume is so high.