There are three main things to consider.

(1) Safety against the possible permanent loss of capital.
I think both are fine on that front. I consider Berkshire to be as safe as an index, but some people would disagree, saying the diversification of an index gives a little something extra.

(2) Rate of value generation
I continue to assume Berkshire will rise in value at around inflation + 7%/year for the next 20+ years. Possibly 8% if we're lucky, but probably fading a bit. Recent results have been better than this for the last several years, but I consider that to be a string of luck that may not last.

QQQE has risen in value at around inflation + 8%/year, plus about .5% dividends, for ages. Pretty much since 1997 (the start of my data) but particularly so since 2005. Even if you pick the most pessimistic amount of history, the number is around inflation + [7.2 to 7.5%/year] + .5% dividends. BUT...(a big but)...there is no truly logical reason for this to be the case. It's only by convention that the fastest growing firms tend to be among the Nasdaq 100 list. It's not a law of nature, and in fact contravenes a number of investment theory axioms. (both QQQ and QQQE are merely the 100 largest firms by market cap listed primarily on the Nasdaq exchange, excluding financials). As a result, the good performance could change to ordinary performance at any time.

(3) Valuation level on purchase day
Berkshire is a little more expensive today than its average in the last 10 or 20 years, but not hugely so. On the order of 10% high. The current situation for QQQE isn't all that much different. On the order of 20% more expensive than usual, perhaps? Not nearly as stretched as the S&P 500.

A valuation that's richer than usual by 10-20% isn't nearly enough to say "you'd be a fool to deploy your capital now, you really oughta wait". Since both are safe and growing in value, likely the worst case for the long run is just a flat spot for a while, with uncertain timing.

That being said, my gut feel is that within 12-18-24 months both of these will be available at valuation levels that are at least somewhat cheaper than average rather than more expensive than average. But it's not usually a good idea to base investment decisions based on the gut feel of some rando on the internet. I think I currently have my highest ever cash allocation, as a percentage of portfolio value. So maybe I'm just rationalizing my position.

Jim