Both are significantly harder in my opinion both in terms of the physical stamina required and the exposure. To me, Russell is a relatively short hike. Mid Pal's hike to the base is quite lengthy and the talus slog after Finger Lake is quite tedious. Your trip will be a lot longer than Russell if you plan it as a dayhike. If you backpack, camp at Finger Lake and not Brainerd, you'll thank me when you compare the two in person. I also think the exposure on that one is much more intense than Russell.
I read that there is a Class 2/3 route up Sill but I've never been there. The time I did it was via the Swiss Arete during a backpacking trip which included Temple Crag. I descended via the North Couloir which is supposed to be Class 4; hated it. Tons and tons of loose talus and rock. I would not want to be below anyone if I go up that way. Even getting to Glacier Notch was a pain. I didn't bring crampons and there was intermitent ice up there, tedious and sandy in parts without ice. Be careful on that one. When I came down, the ice holding the talus together was melting and it took several hours of nervous boulder hopping before getting back on trail. The views from that one are absolutely fantastic though.
I'll find some pictures and post later tonight if you're interested.
