Have these compositions of block ciphers the same security? I'm interested by the compositions of the block cipher DES, instantiated with independent keys $k_1$, $k_2$ and $k_3$.

Are these 3 compositions equivalent in terms of security?
$$DES_{k_1}(DES_{k_2}(DES_{k_3}(.)))$$
$$DES_{k_1}(DES_{k_2}(DES^{-1}_{k_3}(.)))$$
$$DES_{k_1}(DES^{-1}_{k_2}(DES^{-1}_{k_3}(.)))$$

I'm also interested in the same question with two iterations (instead of 3). Are these equivalent in security?
$$DES_{k_1}(DES^{-1}_{k_2}(.))$$
$$DES_{k_1}(DES_{k_2}(.))$$
Yes, you can reasonably expect that these will provide equivalent security, if you choose all keys uniformly and independently at random.  The decryption operation is basically the same as the encryption operation, so it would be extremely surprising if there was any significant difference in security among these.

(Of course, if you don't generate the keys randomly, then this all goes out the window.  For instance, $DES_{k1}(DES_{k1}(\cdot))$ has very different security properties than $DES_{k1}(DES_{k1}^{-1}(\cdot))$.  I suspect this doesn't need saying, but I'm listing the caveat explicitly: it is important that you choose all keys uniformly and independently at random.)