Hello welcome to Smogon! I would recommend refraining from making threads like these for simple/general questions and answers, since we already thread for this and you need permission from a moderator of the sub-forum to make a thread, the simple questions thread can be found
Here.
To answer your question, making an in-game Ubers team requires a lot of work, compared to the effort for an OU team having to Soft reset for desired IVs / Natures or transferring from previous games exclusives like for example, Defog Giratina can really amount, if you're trying to get into competitive on the 3DS I would recommend going for an OU team (since you can breed / capture a majority of the pokemon much readily available) unless you are truly dedicated, hope this helps.