Best all round Neutral Density filter to get?

I can only really afford to get one of these & I see there are x2, x4 & x8 types available. I'm guessing the x4 would be the wisest choise but I thought I'd ask here first. I'm buying it to use on my travels & I imagine it'd be used mostly for landscapes & waterfall scenes.

Thanks for any advice.

I got a .4 and it gets a reasonable amount of use. However, I'm often wishing it was darker, and never wishing it was lighter. I think for me the .8 would have been a better choice.

If you want one for the slow water affect then darker is better. If you just want one for reducing the light levels some on a bright day then a lighter one (or a polariser) may be a better choice.

I use the 3 stop Hoya ND and last week whilst on holiday I was photographing waterfalls and cataracts and really needed the extra stops.

If you have a polariser then this is equivalent to a 2 stop ND, which may serve your needs, but I'd still go for the 3 stop personally

ive got an nd4 and dont find it that effective , i just ordered a nd8 so hope it will block out even more light , plus you can always stack them

I have a ND8. I struggle to get 1 sec exposure even with ND8 on a bright day, so I guess anything less than than may not be very effective.

Unfortunately there's different ways of specing ND grads used by different companies. Such as .3,.6,.9... or 2x, 4x, 6x etc. You can see this in the answers above. I don't remember exactly the differences. But what I read is that for general purposes a two-stop grad is recommended and that means the same regardless of their notation. But some recommended a three-stop for digital cameras. I have a two-stop, but don't have enough experience with it to have an opinion yet.

You are right, its better to express in terms of stops. My ND8 is a three stop grad.