[kereru67]

There are three schools of thought, top of nothing, MUD and low. They all have advantages and disadvantages.

If playing top of nothing you should in principle play your second best card on round 2. Then if your partner is paying attention they'll hopefully notice that the low card is missing and deduce that you're leading from 3 rather than 2. A downside is that even if your partner is clever enough to do this, declarer can easily mess up your signals by withholding a low card. Also, it gives up the remote chance that your 9 or 8 spot might be worth something after an honour pile-up.

MUD doesn't solve either problem. The initial lead is ambiguous and could more easily be mistaken for a 4th best, especially from a holding like 832, and the follow up card might not resolve the ambiguity. Not really a fan of MUD at all.

That leaves bottom, which is probably technically the best option, but the least popular. Perhaps the best way is to use 3rd and 5th best leads, and give up on the idea that a low card promises an honour? Also, is there any difference when leading an unbid suit and leading your partner's bid suit?

[sfi]

MUD clearly gives you the most information, but frequently one trick too late.

Against NT it is generally considered more important to signal strength rather than distinguish between two and three, so it's fairly common to lead high or second high from weak holdings against NT. It's more important to give count against suits, so MUD and low from three are much more common that top. This is one of the reasons many people play 3rd/low vs. suits - as you point out it just fits in nicer. That's not to say you can't lead low and play 4th best, but now you have confusion both in count and honour strength, so it starts to get hard for partner to figure out the hand.

If you haven't supported partner's suit then the leads should remain the same. If you have (showing 3+), you may have the luxury of leading high from a weak holding.

[kereru67]

Hopefully we can at least put to bed the myth that you always lead the highest card of your partner's suit... most of the time you lead the same card as you'd normally lead if it was an unbid suit. only reason to lead K from Kxx is if there's a pre-empt and you want to check out dummy

[Stephen Tu]

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That leaves bottom, which is probably technically the best option, but the least popular

Is it least popular? Must be a regional thing. Here in the U.S. it's overwhelmingly popular among better players. The only ones not doing so I see are the ones adopting Polish style 2nd/4th leads. MUD is exceedingly rare.

But lead high from 3 small (not 3 to honor) if you supported in the auction, this can help not losing to declarer's singleton K/Q on some hands where it costs.