I've done NW/KL into BCN and then Air Europa to PMI in paid biz. I think it's a fine airline with generally new planes and OK service, although business on the shorter routes mostly gets you lounge access and no lines.

Coming from the US, the easiest connection is BCN. In addition to it being a new and recently expanded airport, this routing avoids the mess of transferring between terminals (several miles apart) in MAD. Smaller Spanish airports generally aren't much with few lounges or other amenities.

BCN is also a wonderful city for a stopover, much more interesting than MAD. Valencia is also pleasant but can be very hot and humid.