What ND Filter(s)?

[GSXRMovistar]

Looking to try something new photography wise and wanting to have a go at some landscapes, more specifically long exposures incorporating the typical sea/water views.

So recommendations and info on ND filters wanted please, what strength, what brand, variable vs fixed or anything else worth considering?

FYI will be used on my Tamron lens which takes 67mm filters

Many thanks

 

[GSXRMovistar]

Thanks chaps, and from my little of reading around would also agree on avoiding variable.

 

[GSXRMovistar]

I bought a 9 or 10 strength Gobe and it didn't just darken photos but altered the colours too. I wanted a Hoya as have their UV filter but was pushed for time.

Oh...I grabbed a Gobe 10stop based on reviews which seemed positive. Will give it a test this weekend and if crap it can go back.