Requirements for a tight end depend heavily on the system being deployed. It's almost a necessity to find the athlete who best fits your system of football.
There are those who believe that a tight end with ballast and strength and girth is key to their offensive system because he has as important a role as a blocker as their is. If the tight end can block a defensive lineman on the edge of the offense, then you automatically have a running game just with that single feature. If the tight end can block those defensive linemen, who are know being placed on tight ends where some years ago they weren't, then the entire offense has a focal point from which to work.
That athlete can dominate. He is bigger, stronger and naturally is not going to be as quick and agile as the other type of tight end. So naturally you then fashion your passing game with him in the vicinity of linebackers. With that in mind, he must have soft hands and the ability to absorb a ball as he is being hit. With virtually every pass, he is going to be hit almost simultaneously with the catch. So soft hands, being able to absorb the ball while being hit, is key.
This tight end does not need to possess great speed. The 5.0 time in the 40 will get the job done. The shortcoming to that is that he is not going to be able to clear defenders on certain pass patterns to help other people. But that is not that much to give up if you have the blocking.
The other extreme would be the Brent Jones type who is a major factor all over the field. He is in a position to go anywhere quickly, across the field, to the outside and down the field. He is going to bring people with him or find openings in defenses.
In this case you need the great hands, the body agility and a lot of the characteristics of the wide receiver. But probably more girth because more passes are going to be caught around linebackers and probably even defensive linemen.
Now when you get to blocking with this person it will be all technique. He is going to have to develop those techniques that he can use with reasonable effectiveness against defensive linemen and linebackers. His ability to absorb and learn technique is critical because he is not going to be able to play mass against mass.
Now there is one more type of tight end -- the great, all around type who is a Hall of Fame type. He is so gifted that he can do all of the things you would usually require two types of tight ends to do.
That type of player makes this a unique position in the NFL. One man who can do all these things, the great, all around tight end becomes the essence of the National Football League. And there have been very few -- John Mackey, Mike Ditka, Jackie Smith, are the only two who have made the Hall of Fame.