That's an impossible question. Do you mean trendy (which also means the bag will no longer be "hot" when the trend ends)? Do you mean classic? Do you mean best-known or carried by celebrities? Do you mean most expensive or highly respected?
"Hot" is different for everyone and every season if you go by fashion magazines, so it is useless to try to "keep up." A person could easily end up chasing their tail. I say buy what YOU love, and like Compass Rose said, your bags will always be hot!