|FUCK THIS SHIT|
First off, let me start by saying that this thing never helps me dig out of a land-pocket, or to find land when I desperately need it. In this scenario it only digs me one card deeper per turn, which often results in three or four turns of me seeing two of the same cards every single time, with only one new card (not the land I need!) each time.
Even die-hard advocates for the Top will agree that what usually makes the top worthwhile is lots of shuffle effects. That way, if you Top and don't like the top 3 cards, you crack a fetchland or whatever your shuffle effect is, and look at a completely new set of 3.
I get this in theory, really I do. It's just that in practice, this almost never proves relevant to the situation at hand. 9 times out of 10, I'm stuck using the Top to try to find my GD shuffle effect, which seems to defeat the purpose, if you ask me.
Then there are the times when I'm forced to tap the top to draw a fetchland/rampant growth because I desperately need the mana... but then I just shuffled my Top into the library. Which again seems to defeat the purpose. You might be tempted to argue that point by saying "well, in that case you just leave the top alone and wait until next turn to draw your mana-fetching shuffle effect!"...
Bullshit. I've literally never been in a situation where I could AFFORD to wait until the next damn turn. I need that damn mana NOW! To that, one might suggest that in such dire straights, flipping the Top for the land is clearly worth shuffling the Top into my library, if I do in fact need the mana that urgently. Well, yes, this is quite true - but it actually serves more as an argument AGAINST the Top.
If you find drawing an Arid Mesa right away to be worth more than keeping the Top around, I'd say you're probably better off having another land or a rampant growth effect in that slot rather than the top.
One of the big gripes against the Top, amongst its few detractors, is that it's a time-waster: Between constant end-of-turn fiddling plus the fact that running the top influences people to play a god-awful number of shuffle effect, having the top out drags games out needlessly.
I honestly disagree with this complaint, in general, because most decks I see run a shit-ton of shuffle effects anyway, even if they don't run the Top. Sure a few players out there will go a bit overboard with shufflers just to maximize their Top advantage - but those decks are probably running Trinket Mage to find the Top and that's a slippery slope to d-bag town anyway...
That all said, I still think it can be cumbersome and I find, personally, that even if it doesn't slow the game down as a whole all that much, it often slows ME down, as I'm always trying to keep 1 mana open to peek at the end of someone's turn... which can really have an impact early on in the game, as you need to be developing at least as fast as everyone else. Falling behind early can easily spell doom later on... Top encourages you to effectively cost yourself one early land drop.
Sure, you might say a "good" player won't waste crucial development mana on the Top - he'll wait until he can afford the mana to start using it. I can certainly understand this veiwpoint, but it makes me wonder why you'd want the Top in the first place if you can't even start using it until later on? Surely by that time you could afford to just cast a real draw spell...
This line of argument implies that the Top is only good mid-game or later... you shouldn't be wasting mana on it during the early crucial turns. But seriously, if I had to pick between a late-game, top-decked Sensei's Divining Top or an Oona's Grace, I'd pick the Grace 9 times out of 10.
For that matter, I would almost always prefer to have an active Crystal Ball on the table over an active Top. Both cards are designed to help you dig for something relevant and improve card selection. In that regard I feel Crystal Ball is vastly superior, because it actually lets you dig where SDT is like trying to dig a hole in sand - it just keeps filling back up as fast as you can shovel. It's actually painful to me to activate the Top, see three useless cards and not be able to do anything about it. With Scry I can just put them on bottom, and never have to look at them again (this game).
Sure, Crystal Ball costs three GD mana, doesn't protect itself from removal and has no built in way to get a card of the top immediately... but the simple fact that it can dig me out of a mana pocket far, far faster than the Top can, or dig me to a needed land equally as fast makes it far more valuable to me. Even still, I rarely find room in a deck for Crystal Ball, so the poor ol' Top just doesn't even stand a chance.
One point I will readily concede: Having both Top and Crystal Ball on the board at once is a VERY delicious and potent engine. Also, Top is pretty damn good in artifact/combo decks (if you're into that sort of thing).
It's not that I don't feel the Top is worthless in EDH. It's just that it's not the "must-run" everyone else thinks it is. Certain decks will absolutely be happy to play it, but many more don't really need it - it's just overrated and overplayed. I'm not the only one who thinks so, either... my buddy Chad quit playing it long before I did, and I argued that it was essential at first... then I started paying attention to how often I was failing to get the expected benefits from it, or how often I was lagging behind because I was sinking a single mana into it every turn...
I slowly, hesitantly even, started taking the Top out of one deck, then another. There wasn't a single deck that felt worse off without it, and many just seemed better without it. Soon I was running ZERO Tops across the board, and I haven't missed it since. I did run it in my shortlived Sharuum deck, as it has many specific interactions that made it totally bad ass... but outside of that one deck, I don't feel like any EDH deck I've ever built would be significantly improved by the inclusion of the Top.