Since, ship travel was the only alternative to land traveling. Was it considered safe and reliable by the ancient Romans? Which form of traveling was more preferred? And I am asking about normal civilian travelers here, not cargo or military.
Sailing was the primary mode of transportation as it was often much faster than land routes, particularly for cargo, into the fifth century in the Western Med. and substantially later in the Eastern. Stanford's ORBIS project can give you a rough sense of travel times, though these data are to be used with caution.
As is very evident from this map here of known shipwrecks in the Mediterranean from 1-1500 (through 2008), almost all ship travel occurred within sight of land. Wrecks seem to have been common though not precisely frequent, though it seems any hesitancy due to risk was more than overcome by the time savings.
Further literature:
Ship travel was very safe in the Roman period, evidenced not only through the large investment in maritime infrastructure seen in various port cities such as Portus or Caesarea Maritima, but also in the wider development of coastal zones such as southern Turkey, where sea lanes allowed better connectivity than land routes did.
On the topic of shipwrecks occurring within site of land, it is important to remember the dangers of using shipwreck data as absolute fact. First, known shipwrecks are not representative of all shipwrecks that ever occurred - only the ones that have been found and recorded. The map of shipwrecks, first generated by Parker and later augmented by McCormick and others, demonstrates that most known shipwrecks are found where sport diving is common, such as southern France and western Italy. The North African coast, meanwhile, has very few wrecks documented despite its massive importance as an exporter of ceramics, wine, oil, and grain. For further reading and cautions against this data, you can see work by Andrew Wilson in the Journal of Roman Archaeology 2009 as well as in W. Harris and K. Iara (eds.) Maritime Technology in the Ancient Economy (2011).
Pascal Arnaud's (Journal of Roman Arch 2007) work on sailing routes and wind patterns is more indicative of the realities of the Mediterranean, where seasonal winds and currents had more of an effect on routes than sight of land.