You might want to wait for Lost Empires Immortals if you choose to get LE.
Anyway, I have LE (and testing Immortals - but am under an NDA for it's info), and honestly I love both LE:I and Sins equally. LE (LE1, not immortals, though Immortals is the sequel AFAIK) has good performance and a great deal of combat, large empires and it's all turn based, though you cannot control the battles like SEIV or Sins. LE does also feel lik a turn-based Sins free roam movement to me at times.
Sins is...... well... theres a lot of posts about it already

Both are a good buy, but it really comes down to rather or not you want a TBS or an RTS with a bit of 4X.