For Cello (Solo):
Low position repeated four-note scale patterns are a pain on cello due to the fingering system. (1812 overture near the end)
For the same reason, chromatic passages are somewhat easier on cello than violins and violas.
However as you go higher up, Scales and then ultimately arpeggios get easier to play as a result of finger distance change.
Double stops up to a octave are usable throughout the range.
Tenths start about from F# (minor) or G (major) (on the C string) as the lowest notes.
Repeated thirds involve a lot of shifting. best to do it in higher position for fast passages. However, this is still quite difficult but a competent cellist should be able to play with some practice.
sustained triple stops require that some the upper notes be about an octave higher than the open string it's played on. This will still be played forte though.
Fast multiple stops can get a bit clunky and more percussive due to the bow pressure.
Fast alterations between natural harmonic and open string in one bow are impossible unless the left hand plucks after playing the harmonic. If the bowing is separated, This still could be a problem in low dynamics.
Forced harmonics are much more agile than either natural or artificial harmonics as they are fingered like normal notes. This still can not be played too forte though.
Don't overuse the A string for solos. For some reason a lot of composers love it, but it just sounds to harsh especially in lower positions. Dropping a melody down an octave is an option thus.
High position fifths are harder than sixths, thirds, octave, and tenths unless there is a chance to use the thumb (Shostakovich Cello concerto no. 1 first mvt. near the beginning)