I'd go with SH4 first as previously suggested. Be advised, both games have certain glitches and bugs (as I'm sure you'll read about elsewhere in the forums). Try vanilla SH4 then add some mods (I'd recommend TMO1.9 and Run Silent Run Deep (RSRD) but I'm biased, LOL). Once you're comfortable with SH4 then try SH5. If you prefer the Pacific and a U.S. sub then SH4 is the only way to go. If you prefer a U-boat then you now have a few choices (for good or for bad,LOL);
1. SH3 with GWX mod (an excellent version and despite the lesser quality graphics does a great job of simulating the Atlantic U-boat war IMHO although there's no wolfpacks modelled).
2. SH4 U-boat add-on - can't speak to this as I only use SH4 for the U.S. Pacific experience but there are many positive comments elsewhere in the forums regarding the Operation Monsun mod.
3. SH5 - the latest but not necessarily the greatest. U-boat action in the Atlantic with a 1st-person/RPG perspective. Lots of bugs and complaints but you can decide for yourself.
