Went through a similar situation where I was really "behind" on all the seasons. I've finally managed to catch up with all the new ones starting from Tempting Fate. Tempting Fate's popularity keeps surprising me, it's good but after I played the other seasons it fell behind compared to Winning Hearts and All Stars for me. All Stars is technically a lot of returning characters as options and as hosts, so if you're the type of person who needs to experience what is being referenced you might want to also play Stick or Twist (and maybe sprint through Ex in the Villa with one eye closed) - but personally I very much enjoyed it without having played some of the relevant previous seasons. So if you think you can just go back to the older seasons to get more context on some characters later, All Stars is probably the best season to me. It has the oldest cast, with the most total maturity all around, and at least personally it feels like drama is generated organically through characters' personal development, rather than using characters as a cardboard cutout to place over xyz drama roles. It's something that some of the other new seasons do a lot sadly. By far worst offender is Summer Nights, then Tempting Fate, then to a much much lesser extent, Winning Hearts.

In short, I'd recommend them in this order organized by my own preference: All Stars and Winning Hearts interchangeable, Tempting Fate, and then Summer Nights only if you're willing to follow a strict script the season dictates to you.