I've always liked Fleet Boats. Played Silent Service on a Commodore 64 with a monochrome screen....ughhh.
Unfortunately, when shopping for a subsim a couple of years ago, I figured SH4 wouldn't run on my computer, so I opted for SH3. A decision I have never regretted.
We got a new rig last spring, and I bought SH4 in August for my birthday, skipped playing stock completely, modded it(have tried both TMO 1.8 and RFB 1.5 +RSRD), and have enjoyed it quite a bit.
I will continue to play both games as the mood comes upon me. Both games have their good and bad points. I think I lean a little more toward the challenge of the Atlantic though.