Apart from the Jagers I wouldn’t put the Hessians on a par with the British combined lights and grenadiers. Most of them I would put on a par with the regular British battalions, though there seems to have been a perception among the British that they were ‘slow but steady’ and better kept in reserve because they were unsuited to the nature of combat in America (there is an idea that they were less inclined to form loose files in difficult terrain than the British were).
British Grenadier rates the Hessian Jager Corps as ‘Elite’ (putting them on par with the post-April 1776 combined grenadier and light infantry battalions); the German combined grenadier battalions and the best line battalions (such as the Hesse Kassel Bose regiment at Guildford Court House) are rated as ‘Line’, putting them on a par with regular British Infantry battalions. The majority of the Hessian line units are rated as ‘Second Line’ putting them on a par with inexperienced British line and the ‘less good’ Continental regiments.
However, the low rating of the Hessians in these rules seems to have been done in part to make them move more slowly on the battlefield. There was a view among the British that the German troops spent too much time dressing their ranks and preserving formation (in terrain that made this very difficult to do). In British Grenadier lower quality troops have to pause more often to avoid becoming disrupted. So this rating is more to do with maneuverability than morale.
If you are just thinking in terms of morale then I would rate the majority of them as ‘regular’.