If we talk practically, UCEED and JEE and entirely two different entrances with different objectives. UCEED is an entrance which aims at listing out the candidates for Bachelor of Design program at IIT's and certain other colleges that accept the UCEED score.
Whereas, JEE primarily aims at shortlisting students for the advanced exam for admission to IIT's, NIT's and certain other colleges that accept the JEE score.
The two entrances even though help the students get admission in IIT's but for entirely different programs that are no where interlinked. UCEED is for B.des while JEE is for Btech. Therefore, there are no particular concrete Basis on which the two can be differentiated upon to determine the difficulty levels.
Both the exams are national exams and a tough nut to crack. Therefore, I cannot adamantly say that the other is tougher is tougher or easier and they are linked to entirely different disciplines.
