Maybe it also depends on how much weaker the opponent is. Agains

Of interest here might be Tim Taylor's lates article, "How to defeat a weaker player" at the jeremysilman.com site.  http://www.jeremysilman.com/chess_true_combat/041001_true_combat_beating_weaker_...

This is just part 1 but I gather he may have an outlook similiar to John Cox's.  Consider this excerpt, "When you are playing a weaker player, you don’t need subtlety, you don’t need brilliance, you definitely don’t need quiet positional openings – you need WEAPONS OF MASS DESTRUCTION!"

The article finishes with (after presenting a game where IM Taylor lost to an expert player), "Of course, most of the time I do succeed in this task, and in my next articles I will explain the best and simplest ways to defeat the lower rated player – and avoid this month’s disaster!".

Should be interesting.

A quite difficult decision to make. I play the Dutch Leningrad also against weaker opponents (as I play it simply against everybody).
Main reason: it is - by far - the opening I understand most of.
But on the other side, when playing the Dutch Leningrad against 200 points lower rated opponents, I always sit there like on a heated chair. what, if my opponent is prepared very well for it? I mean, every risky opening has its 3 or 4 positions that are considered less favorable or that are difficult to play. Compared with the NI/QI I could be quicker in an uncomfortable position and the position could be by far less playable. If White knows what he is doing, what is luckily a rare thing. In most games I like the Leningrad Dutch positions very much.

Main reason for my decision could be, that my fear to meet a well prepared opponent in the Dutch Leningrad is by far lower then my fear to play in the NI/QI 4 or 5 hours long positions, that I dont like and that are dull and where I must - even against weaker opponent - enter a long, long rook endgame.

The answer is simple. You should play whatever opening you know best!

But I agree there may be a difference with regards rating catergories... the situation between a 2700 vs 2500 is diffferent with 2200 vs 2000. In the sub-2200 category, anything and everything can work.  But I'm not so sure if a 2700 GM can beat a 2500 GM using the Berlin Ruy.

When I wrote my initial response is was precisely Webb's advice that I was thinking of.  Perhaps this isn't the traditional line of thinking however.  I know that often when I've tried to play solidly against stronger players it's rarely worked out for me.  Perhaps that is result of my particular syle and other shortcomings.  Maybe the choice depends on what level of Chess expertise were talking about too (1800 elo versus 1600, 2000-1800, 2200-2000, etc...)?

I would say that's no easy answer, either choice will be the best for some people under some circumstances. Personally I would tend to play the more aggressive option with Black, and the safer option with White. This is mainly because I'm a better attacker than I am a grinder so I find it tough to beat weaker players with Black if I've given them the chance to stodge it up. On the other hand with White it's a lot easier to generate winning chances even if Black tries to be solid. It's also the case that the stronger player is more likely to know a good line against a sharp and aggressive, but slightly unsound line.

If your repertoire against d4 includes 2 openings, one aggressive (lets say Modern Benoni/Leningrad Dutch), one solid (e.g. Nimzoindian, Queens Indian, Queens Gambit) - what one you would most likely choose against a weaker opponent?