I don't know much about tablets but I guess that like with any other device you'll have to narrow it down according to your preferences and needs. Do you need a headphone jack? Do you need it to be powerful for some hardcore emulation? Do you need some uber fancy screen resolution or refresh rate? What kind of size are you looking for?
Once you nail down what you need and find a bunch of models that fit your criteria then it's just a matter of sorting them by price and availability. It's also good to look up manufacturers to see if their track record has any issues. For example ASUS has become somewhat notorious in recent years for screwing people over on warranty. I don't even know if they make tablets, it's just a general example. Another thing to watch out for is if the manufacturer tries to play that stupid 'forced arbitration' game. Basically, companies are trying to force you to agree to waive a bunch of your rights as a customer just so they can screw you over when an opportunity to do so arises. It's highly illegal in the EU and you'd probably have a fairly easy time winning that battle but do you need another headache to deal with for a damn tablet?
I don't really have much to say beyond that. Maybe once you find a couple models that interest you you could post them here or in a profile post so that more knowledgeable folks can offer advice.