IMO, tech is unlikely to be a bad sector going forward since the p/e ratio is the around the same as of S&P 500 and significantly lower than the Dotcom bubble. Diversification isn't always helpful - it didn't matter how diversified you were during the 2008 stock market downturn, almost all sectors dropped by over 50%. As an example, if you held FDN right before the downtown, you're portfolio would've dropped by almost the exact amount as if you had held S&P500 even though FDN only has 42 stocks compared to 505 of S&P's. Also, FDN recovered significantly faster than the S&P500 and crushed it in returns going forward. FDN might not repeat the same performance again but I'm confident that at least Nasdaq will significantly outperform S&P500 again like it has been for so long, there's no reason to think it won't. It's not in a bubble like it was 2 decades ago, everyone learned their lesson.When you say "yield" I presume you mean highest returning, as in, total growth or total return.
Nobody can predict the future. The general thing we know about stock investments is that, on average, stocks tend to increase over long periods of time such as 20 years. But there are different sectors in the stock market, and some will gain more than others. For example, tech gained a lot in the last 10 years. But, in the decade previous to that tech actually had the worst return, and the best stock return was something else, maybe the utilities sector, or foreign/emerging markets.
If you had bought one of these tech ETFs 20 years ago, you would have seen absolutely horrible performance.
It changes every decade. We really can't predict which sectors will be strong and which will be weak. It sounds like you're trying to target the tech sector, anticipating that it will continue growing at the strong pace it's had in the last few years. It may do that, or it may turn out to be a horrible sector in the next decade.
The general approach to tackle this problem is to make diversified investments that include all sectors. Why? Because that way, you capture the general effect -- that stocks on average go up over time. This is a better way to go than betting on a specific sector.
Among the ones you listed, QQQ is the most diversified, but it's still awfully heavily concentrated in tech. In my opinion you'd be better off with a broad US market ETF such as IVV for the S&P 500 index, or you can hold ZSP (trades in Canada in CAD) which holds the same stuff.
Since June 2000, according to my charts, QQQ has returned +162%. SPY has returned +203%. So that's 19 years of the S&P 500 outperforming QQQ. Since the previous tech bubble peak, QQQ has not caught back up to the S&P 500.I'm confident that at least Nasdaq will significantly outperform S&P500 again like it has been for so long, there's no reason to think it won't.
I'd recommend you pick QLD (Nasdaq-100 2X Bull) over SSO - it outperforms UPRO yet is less riskier. It also survived 2008 and has a Canadian version, HQUI think long term positions in leveraged ETFs can work out, provided that the ETF does not completely blow up. For this reason, if I was going that path, I'd stick to the lower leverage versions. The higher leverage versions are more likely to completely blow up / unwind. The higher leverage ones also have worse tracking in highly volatile markets.
One I have considered holding long term is SSO, leveraged S&P 500. This one survived the last financial crisis, so there's some reason to think it might not blow up in the next one as well. 10 year annualized return of 23.36%. In 2008 it only dropped 68%, which isn't too bad.
It's actually something I may open a position in once there is a significant market correction. I would consider it extremely high risk, since it's an exotic ETF. But at least it survived 2008.