An omni you are able to run in the optimal configuration is going to be far better than one you can only run in a compromised configuration.
I'm partial to DPA 4060/4061. For me they represent an omni price/performance sweet spot. But in addition, and for the reason stated above, their super small size and minimal weight is crucial because I could not otherwise achieve an appropriate spacing configuration supported by a single stand when open recording outdoors, at least not easily in a visually unobtrusive way. For two-channel use alone outdoors, I'd space omnis no less than 3'. If they are to be mixed with a center microphone or microphone pair, better to space them 5 or 6' (basically double the spacing used alone).
A higher quality omni, used in a compromised setup with less A-B spacing, will be a step backwards rather than upwards in the quality of the resulting recording.