LPG used to be 100 octane, but now, with all the crap that is mixed in with it, it can be anywhere. The usual rating is 98 octane, but I wouldn't trust it too much. I personally believe it is on the same par as unleaded, about 95
I had a 351 Cleveland that was built as a gas engine @100 octane. But I had to lower the compression as it kept on pinging.
I believe you can get bad batches of gas, as you can petrol. Again, use high volume servos.
, no brand is better than another.