The current Monero median block size (last 1,000 blocks) is 286 bytes. The median transaction size is slightly less because some block include multiple transactions. The current median BTC transaction size is 260 bytes.
http://moneroblocks.info/stats
Monero median (not mean) block sizes are important since they influence the dynamic block size limit (which is 2x the median block size over the last 720100 blocks).
Note that median transactions sizes also include coinbase transactions which are relatively small compared to non coinbase transactions. As transaction volume increases (with non coinbase transactions growing as a percentage of total transactions) the median transaction size will therefore increase as well.
When looking at mean or maximum sizes Monero transactions can become larger due to the possibility of a very high mixin and many outputs.
Pruning is possible for Monero. In fact a pruning branch already exists for Aeon which began as a Monero fork.
RingCT will raise transaction sizes for Monero but to a lesser degree than a Confidential Transactions implementation would raise transactions sizes for Bitcoin.