As for timeframes for entries, if lower timeframes mean tighter stops, than as low a timeframe as possible so long as you can find a good trendline. In practice, I think the time available to sit and watch the charts may well be the determining factor.
Personally, I have less confidence in avoiding false breaks of trendlines on the lower timeframes such as M5 and lower. That is just an opinion and I don't have any statistical data to support my bias. I should preface my comment with a disclaimer that I am in the US and my observations are based on the NY session. It has been many years since I stayed up late to try and scalp a few pips during the London open.
I try not to fall victim to my bias because even if the lower timeframes do have more false breaks, that is not a negative since a trader can generally have a tighter stop the lower they go on the timeframe. That tighter stop should equate to less risk (in pips), which would lead to a larger reward relative to risk. A higher reward:risk would offset being stopped out more due to any false breaks.
As an example: Trader A shorted GBPUSD with a 30 pip stop, basing his entry on the H1 timeframe. Trader B shorted the same pair with a 15 pip stop, basing her entry on the M15. Trader B could be stopped out for a 15 pip loss and re-enter with the same 15 pip stop before she has risked the 30 pips that Trader A put at risk.
If both traders put the same % of their account at risk on each trade, Trader B would come out ahead as far as % return on the account. (Both traders exit after a 150 pip decline. The 30 pips risked by Trader A equated to 1% of his account, with his profit on this trade equaling 5% of his account. The 15 pips risked by Trader B also equated to 1% of her account. She netted 135 pips with her total profit on this trade equaling 9% of her account.) Like my wife, Trader B is one smart lady. Too bad my wife doesn't trade, she could have saved me many years of trial and much error.
These examples go back to Nigel's statement about using PAST to obtain longer timeframe reward (big) with shorter timeframe risk (little), which effectively multiplies your reward:risk. This supports using the lowest timeframe possible with a good trendline so as to minimize your risk and maximize your reward. And that is the best position for which a trader can hope.
Jonathan