What size wires do you have between the two batteries?
Some people advocate for connecting to the + post of one battery and the - post of the other battery. Only matters if the wires connecting the batteries is undersized. If you have size 8 or larger (6, 4, or so) between the batteries, it won't make a noticeable difference. The batteries will equalize very quickly across the large cable. Now if you have a 12 guage wire, or smaller, for jumpers, then all the little electrons have to get in line and file over the narrow bridge. Think about the traffic backup that occurs when one lane of the interstate is closed. The batteries will equalize, but the one you are connected to will do more of the work.
2005 Trillium Outback w/ 30" tongue extension
1989 Award 730, 30'
2003 PT Cruiser
1998 K2500 Chevy Silverado 6.5 Turbo Diesel, 4X4, ext cab, short bed