Marcus - slightly more effecient Marcus smart. Already one of the best perimeter defenders in the league, he'll max out his shooting at around .430 fg & .310 3fg - averages will be dependent on the team but could see him maxing at around 12 ppg 5 rpg 6 apg and not necessarily in the same season. I can't think of a good comparison with those numbers but also the defensive value.
Tony Allen is not a good comparison because whilst a better finisher at the rim, he wasn't as good a playmaker or 3 point shooter then Marcus is currently. And I don't remember Tony being able to defend 4's like Marcus.
Jaylen - the RJ is not a bad comparison, is like to think jaylen will develop a wider offensive repituare. Both a superior athletes, but jaylen seems more polished when getting his own shot off the Richard Jefferson. An offensive comparison I like is prime Rudy gay, but probably a much better defender and team player. Hopefully he gets closer to a T-mac level, but thats definitely a glass half full kinda thought.
Terry - young Brandon Jennings, young bj could get to the paint, could get his own shot off (albeit not very efficiently). You could argue that terry will be a better defender, and I can see that. Terry is solid defensively as bj was not, personally I just don't see terry as a player with game changing defensive value.