Currently DL seems to be handling operations and IROPs rebooking better than its competitors.

Remember that it's not just a matter of the carrier, but also the connecting airports and aircraft types, with some USA airports being much better at handling snow than others. Smaller planes are more likely to be delayed or cancelled, so that one should avoid commuter planes or RJs where possible.

Finally, it's better to stick to one airline (or one alliance) and purchase the ticket directly from that airline to avoid the finger pointing blame game when something goes wrong, with no one being willing and able to help.

ADDED: Before travel, learn about your basic rights in IROPS (EC261 for Europe, DOT regulations for the USA) and skim your airline's CoC for information about their policies and procedures.

ADDED AGAIN: Research backup plans in advance. Have a Plan B and Plan C at least. If you're expecting problems, check availability on alternative flights early and often. Have some clearly written (hard copy) list of alternative flight details, complete with flight numbers and times.