If you can get the 255 for the same price as the 190 go with the 255. That way if you ever get boosted in the future, you won't have to switch pumps again.
190lph N/A and 255lph with a power adder. Being rich is WAAAAYYYYYY better than going lean. There are also 2 flavors of the 255lph pump: the standard 255lph and the 255lph high flow pump. Everyone has always recommended the high flow pump for power adders, however i run a standard 255lph and it handles the job just fine. Now if (when;-) ) i upgrade to a T-trim with that much more power and boost, i would definetly switch over to the high flow pump.
Always go with the bigger choice; the FPR is going to return any unused fuel. I've been running a 255 in my nearly stock '91 LX with no adverse results for years now, except for a bit more pump whine (as compared to the 190 I had in my '90 LX).
I've got a in tank 255 and an inline 255 running for my setup so I would recommend the 255. I think it's kinda cool to turn your ignition on and have swish sound coming from the back... Intimidation :0