I have a pair of yamaha f150's on my rig. Well proven engines. I have just over 1400 hours on mine. 

 Just bought a new suzi 4 140hp, super impressed. First run yesterday and did 200km for 90l going through all the rev ranges. Very quiet as well. Happy with my decision.

 Huge difference between the Suzi 140 and yami 150. Have had both and yami wins hands down.  My choice would be the yami 150

 Just keep in mind the 140 Suzi is an up spec 115, same 2L block, same ratios just different ecu. The 150 (suzi or yam) are in the next class, bigger capacity block 2.7Lish a de-rated 175 - 200. In saying that i had a 140 suzi on my old boat a 5.7 trailcraft and it was a perfect match. I just know that there are people who put them on larger boats who are disapointed with power. Both great engines just depends on what you're bolting them to. 

dont believe the hype u have to go bigger than the 2 stroke u had on 

175 johno 2  to a suzi 175 4 got me 3 knots extra  -and heaps more out the hole

fuel is less than half and the noise  is not comparable

i miss the smell of the 2 stroke after a long dive   ;p

do it- jsut dont get caught out on installation "extra charges" after they gve u a quote

 140 Suzuki is only a higher revving 115, 1.7 litre in capacity. The Yamaha, whilst a proven, reliable engine, can't match the Merc for Grunt. This, from comparisons mounted on the same hull. The Yamaha has a much larger capacity than the Suzuki, at 2.6 litre. But it also weighs 228kg. The Merc has a full 3 litre capacity, and weighs 207 kg. It is a lower revving engine ( max revs 5200-5800 rpm)  relying on capacity rather than revs to produce the power. I have done just under 600 hours in just over 2 years, nil problems. And I have a 6 year warranty, hours unlimited. 

Mine is pushing a Caribbean Reefrunner. 6.4 m ( measured minis bowsprit and paltforms, weighs 2 tonne on the water fuelled up with 2 POB)  People will automatically say that 150hp is "too small" for that hull, with a max transom rating of 200hp. In most cases, yes. The  few owners who I have spoken to with the 150 Yamaha fitted to this hull feek that it does lack a bit at times. With the Merc fitted,  all you are mssing out on is the ability to cruise over 30 knots. With a top end  of 35-37 knots, depending on fitout, you are using 5000 rpm to hold 30. 4500 sees about 26-27knots with good fuel flow. If you want best economy, anywhere from 3700 to 4200 sees good speed with good fuel flow. 

The following are screenshots from the engine interface, from a recent trip to Exmouth. These are taken in calm conditions, but I seem to get prretty much the same in most conditions. NOTE that i am using nautical miles  the only unit to use at sea, IMO  ) I NM is 1.852 km.  Boat is fully loaded.

I don't have any current screen shots for the lower speeds, but it runs at a steady 1.2 l/NM all the way from 3700 to 4250 rpm. So you can get good speed with no increase in fuel used whatever over a given distance. And before anyone says that isn't good, I'm not pushing some 5.6m forward control boat with no top that weighs maybe a tonne on the water, this boat is 2 tonne on the water.

And for those challenged with speed, 31 knots = 57.4 km/hr

                                                      27 knots = 50km/hr

My normal cruise is around 4000rpm at 21-22 knots. 

Interesting figures above Ranmar.

I have just upgraded my 10 year old twin 150hp 4 stroke Yamahas to a pair of 2020 models. The old had 19 inch pitch stainless props, which I spent a lot on (around $2,500 if I remember correctly).

I measured my fuel economy on the old motors from new and for 946 hours averaged 1.82 litres per NM (both engines combined).  Best I got was 1.62 litres per NM and worst was 2.02 L/NM.  I found the best RPM to be 3000 - 3400, doing 22 - 25 knots depending on sea conditions.  

I've only done 8 hours with the new motors.  Same pitch Yamaha stainless props, but what I see is different and maybe I need to change props.  Seems I need to run at a higher RPM to achieve the same speed now.  Last Saturday I was running around at 3500 RPM for around 25 knots.  For the two trips I have done (first one included a bit of run in), I've averaging near enough to 2 litres/NM.  On face value, this is a bit disappointing, but I guess still pretty good at around 1 litre/NM for each motor.  At this stage its around 10% worse than the old motors.  

BTW, the boat did 44 knots WOT during the prop test, which is fast enough :-)

 well thats interesting belly fish - could it be its still running in 

thought the new motors are better than the old

The figures seem quite good however jury is still out on the new mercs as they haven’t been around long enough. I prefer Yam 

Yep, no jury out on Merc 150's, plenty of history out there now with enough forums highlighting the good and the bad. Unfortunately a poor setup seems to be the reason behind so many arm chair critics ( this is not directed to anyone on here, just my perception of forums) on performance for any of the brands mentioned.

Yeah I’ve read people have had a few issues with them. Yam Honda and Suz have better resale value though  

Like everything SK, you only have to look on fishwrecked for negative comments on yam and suzi's.
I don't agree with the resale value about mercs and I do not own a merc, personally I would seriously consider all the top brands, brand selection may come down to weight, sales, servicing and personal choice.