The Skytrax posts for Heathrow T5 are better on the whole than those for Frankfurt. I personally haven't used T5 yet, but I've been through T4 umpteen times on BA before T5 was opened and they have never misplaced a piece of my luggage, but this happens with all airports; at the worst of times past in the UK security was thorough but at least polite.
Couldn't care less what reviews show, I fly internationally about 85 times a year, I know what I see and experience...
T5 has a particularly bad reputation for losing luggage on connections.