Well, like my friend Cathay747 said, there are 3 engine choices. Now about the little slits, well, both GE and PW engines have them. The difference is, the side of the engine they have them on. Was that KLM picture, by any chance a shot looking at the starboard side? The reason i say this, is because the GE engine has the little
= slits things on the right hand side (starboard so there is no confusion about which direction we are looking from), and, the PW engine has the little slits on the port side. This is true for 767s too. (which uses the same engines in many cases) The other way to tell is that the GE engine seems to be totally flat on its metalic exhaused, maintaining the same angle of decline, where the PW engine sort of changes just a little where the metal texture and colour changes. Also, the PW engine casing seems slightly smaller than the GE.
You can see here in this Qantas 767-300ER, which is CF6 powered, the slits on the starboard side. (the qantas 767-200s are PW JT9D powered, and the 767-300s are General Electric powered. I haven't a clue why the changed engines types between the two types. They seem to like the GE ones though. Ansett's and Air New Zealands 767s are all GE powered.
To compare engines, i just thought i would put a picture of the United 747-400 with PW4056 engines here. As you can clearly now see, both engine types have the slits, just on opposite sides. Thanks to United for operating the 747-400. (i want cheap economy tickets to stay, lets keep flying the 747-400s and not downsize to 300 seaters when the demand is there because its easier to sell the more expensive economy tickets to business travelers). Of course, the best engine of all is the rolls royce one in my opinion. It stick a picture here but it would take too long to download on some peoples interent connections.