Can you elaborate on your goal? (some specifics) You are trying to profit from expected (or probable) "...." move in "xxx" in next Y days. By spread, do you mean vertical spread? Likely you are interested in trying to capitalize on a very short term directional movement or spike in VIX, if so, your time frame may bias your choice. Interesting that the Bid/Asked spread on VXX options is very small compared to those on VIX! Could be due to the increment being 5 cents on VIX vs penny on VXX. -- VIX options have a lot more volume. With some specifics, perhaps someone here with more trades under their belt with these products can provide some insights.