The active orders on some brokers tell you how they got routed (i.e. via "Citadel"). I did some testing, with similar trades. Some of the difference is just f

The active orders on some brokers tell you how they got routed (i.e. via "Citadel"). I did some testing, with similar trades. Some of the difference is just from the commissions structure -- if it's not a percentage of contract price, smaller priced contracts benefit from lower commissions. I was buying and selling long and short strangles and straddles or iron condors. Sometimes strangles with farther out contract legs, at prices like 0.40-0.80, would use Robinhood (simply because I had an account with them, and not every other broker), while nearer contract legs at higher prices on the same underlying would use Fidelity or IBKR. Generally I was entering and exiting, not holding to expiry, so I had 0.65x4+fees = 2.70 in commissions for a given contract pair on Fidelity. Nowadays it'd often be about 2.05 on Fidelity because they let you close contracts under .65 for free. I didn't think to negotiate commissions, but I was surely too much of a small fry for that.