The Expanse also has realistic space combat.
Realistic but the scope is completely different. The Expanse theater is limited to our solar system, so ships are still moving relatively slow. In the Lost Fleet, the theater is across many star systems where capital ships move at around .2C. I can't recall if they ever detailed how fast the ships go in the Expanse, but it was still a considerable time distance to travel between the planets. In comparison, our space shuttle now traveling at 25,000 mph is 0.00004C.
For the most part though, I would recommend The Expanse over The Lost Fleet, but it's not quite right to even compare the two. The Expanse is just a really good story (only a small portion is space combat). The Lost Fleet is all about getting your naval space combat fix in, but it's not life changing or anything. I'm 11 books into the series and still enjoy it.
Looking at my tracked series, here are a few lesser known ones that I have enjoyed:
Iron Druid Chronicles - Kevin Hearne: modern fantasy with comedic flare. All the mythological gods and figures are real (Norse, Irish, Roman, werewolves, vampires, Jesus, etc) with their power coming from humanity's faith. One of the books is focused on killing Thor, mainly because he's a big jerk. All in all, the series is a fun read. Not a great read, but fun none the less. Hearne also wrote the recent Heir to the Jedi novel, to mixed reviews.
Odyssey One - Evan Currie: Future Military stuff. Takes place after WW3 and humanity is starting to venture beyond our solar system only to find we're completely out-gunned. The only thing we have going for us is that our society has evolved from constant war with ourselves, so humanity's weaponry is more effective even though its ridiculously under powered. Again, not a great read, but enjoyable.
Ghost Fleet - P.W. Singer / August Cole: A novel of the next world war. Not a series (yet) and just came out about a week ago. I just finished it yesterday and I found it quite enjoyable. It takes place in the near future and is about China/Russia launching a sneak attack against the US to primarily secure the Pacific for resources. It combines the latest trends in tech to imagine what the war of the near-future (nothing super advanced, more like militarized quadcopters). It has its problems, but I thoroughly enjoyed it.
Edited by treybert