I started Polish here on Duolingo, but switched to Czech when the beta was announced. Compared to Polish, writing in Czech is a breeze :) I am a native Slavonic language speaker and in my language writing is more phonetic than in Czech.
Laughs in Polish
But honestly, I think both have pretty similar difficulties:
Voiced vs. unvoiced consonants (morphological spelling) - same here.
Pairs of letters representing the same sound (historical spelling) - same here.
Not always following the "write how you speak" rule (like words beginning with "j + consonant" or clusters like in "zvláštní") - same here, especially words whose direct pronunciation would be considered hypercorrecting: "sześćdziesiąt" (pron. "sześdziesiąt"), "dziewięćdziesiąt" (pron. "dziewiędziesiąt").
The only stuff we don't have is long vowels vs. short vowels, and here I'm curious - do Czech people consider some of them difficult to spell? (I personally find it peculiar that the length of the vowel may change in various forms of one word, but that's a matter of remembering a word, not of being able to write down a word we know). Are there some words with vowels pronounced long and written as short, and vice versa?
Btw, remember that there is still English and Irish and THEIR orthographies.
And, personally, the most difficult thing to me, apart from remembering where it's í and where it’s ý (and sometimes distinguishing between "i" and "e" at listening tests), is remembering the voiced/unvoiced stuff which is written differently in Czech and Polish in words consisting of the same morphemes.
zpráva - sprawa (case, matter), z prawa (an old-sounding version of "to the right") (this one is actually easy to remember)
s/z - in Polish both are "z" so every time I have to type one of them I have to stop for a while to remember which one I want to use.
Compared to English (or even my native language Dutch), I find it a relief to see how consistent Czech spelling is. Pronounciation is often more difficult than actually spelling the word; especially slurs of cossonants can be dreadful for foreigners to deal with...
Interesting I thought Dutch and German were pretty close but I think German is pretty consistent with it's spelling