The two schools are similar in a lot of ways, but they have very different vibes. LSU is a lot bigger, which definitely adds to it.
I can't speak to the issue of having dropped a sorority previously, and I don't know anything about membership selection. I do know of people who transferred to Ole Miss and had successful recruitments, but they were from community colleges, not other SEC schools. If it fits your timeframe for transferring, the Alpha Phi colony might be something to consider as well, but I have no idea if that might work out for you or not.
I'll also say this:
You do not have to be Greek to have a meaningful or enjoyable college experience.
Even in the SEC.
Even at Ole Miss.
Other organizations aren't going to replace joining a sorority, but there are tons of amazing groups and things to do at the University of Mississippi. If your goal is to meet people and have a good time while getting a solid education, it's entirely possible to do outside of a sorority. That said, if you absolutely can't imagine being in college without being Greek, then I don't know. But only a third of the Ole Miss campus is Greek. There's another two-thirds of the campus that is not, and some of those students even have social lives. Really.
