A tablet can top the iPad, depending upon the features the user wants. Since the customer is always right, it is up to the individual to determine what is the best iPad. Every person wants certain browsers, capabilities, games, apps, software, etc. So I guess we would determine the best tablet according to overall sales.
There are LOTS of tablets out there. Nexus 9, Galaxy Tab, Surface, and even kindles and nooks. I think every tablet has their strong point, as well as their weak point. But the I-Pad has weak points as well. And I think there are lots of tablets better then the I-Pad (My opinion). My favorite tablet is probably the Nexus 9 http://www.google.com/nexus/9/
And that is just my opinion. I love android, but sometimes companies mess with it, put a bunch of crap on it, and ruin the whole software. I like the Nexus 9 because it runs stock android, the original, pure android. Back to the I-Pad, i don't think it will ever fail. My reason? People are just WAY TOO ATTACHED TO APPLE. I mean seriously, before the I-Phone 6+, apple users would say that it is great to have a small screen, and big ones are not as good. After the I-Phone 6+, apple users would say, Wow, how I love the big screen! Some are just not willing to try out other products. Some just grow to attached to them, and they will never let go. This could be why the I-Pad is so popular. And this could be why the I-Pad just can't be beaten. BUT, if people come around, and decide that maybe they could give some other tablets a try, the I-Pad may not be so popular anymore. (this is all pinon, so you can say your own opinions, just don't try to disprove mine).
I honestly don't see any companies trying to out do the iPad. I think that is sad since there is absolutely a market for it. I see a lot of competitors focusing on the lower end and trying to create cheaper devices. After all, the poor have to be able to buy the goods or they don't sell near as many.
Apple has been bringing reliability, easy of use, and beauty to all of it's products ever since it's conception. With that being said, some other companies do make some tablets that might be a little better than the iPad. They have different functions and possibly better hardware, in some cases. However, what puts Apple and the new iPad on top is what they bring to the table. It will work forever and has the brand trust of Apple.
As soon as you come out with something awesome, everyone tries to copy your idea... Which is what creates competition and business. When Apple came out with their new iPad I was truly amazed at all the features and even though there are other tablets out there competing with it, I doubt they have a chance. In my opinion, no one has made a tablet better then Apple, yet. The IOS software they run is outstanding compared to any other tablet in the market even android. Until someone comes out with a better operating system, Apple is there to take the lead.