We are looking at flying to the US from the UK sometime in 2016. We have flown with Delta for the past few years as they have tended to be the cheapest.

We have always booked direct with Delta, (we would never use a third party booking agent) but understand we can book direct with Virgin, KLM, or Air France and still fly with Delta. Am I right in thinking that an upside to doing this is that I will benefit from better EU consumer protection? Are there any downsides to booking with a partner airline. For example, If things go wrong, say due to bad weather conditions, or getting delayed going through security, will it make any difference?

Can we generally select our seats, for free, as we do when we book direct with Delta.

Also, are the seat prices generally the same between all the code sharing partners. Or may I get a much better deal if one of the airlines has a sale?

Sorry for all the basic questions. Grateful for any advice.