We have used both in the past. We took Eagle Pass several times then one year found ourselves in San Antonio so decided to try Laredo (Columbia Bridge crossing--not the one in town) and now we purposely detour to use that one.
It us much quicker to Saltillo, and in fact now we can stop further south than that. It also avoids Monclova, which used to be a Transito Gauntlet run though I have heard that it has improved.
As for time, we always strive to cross early, as soon as the crossing is opens, about 8:00 AM I believe. That way we can get further into Mexico Not really any good overnight places closer to the border.
Last year we had planned to stop in Mazatlan and PV on our way south to Zihuatabejo but were delayed in San Antonio for too long (waiting for a windshield for the coach) so we just headed south.