Oh, I can give you plenty of feedback on this topic based on first-hand experience. I have two machines running the Intel 330 (120gb & 180gb), and two running Intel 520's (120gb each), one of which is in a RAID-0 array with a Kingston HyperX 3k.
There are two themes I would say are strongly evident when comparing the Intel models to each other. First, free space is a MAJOR factor in speed. The difference between the 120gb and 180gb version of the 330 is huge. Second, the 520 drives are much more efficient at utilizing TRIM and managing to keep their write speeds satisfactory even as they start to accumulate data. I would NOT suggest the smaller 120gb version of the Intel 330 to anyone. The performance falls off from the level of the other drives staggeringly fast. I ended up making it the OS drive for my HTPC because I had no use for it in my performance rigs. The 520 seems to be slightly ahead in its 120gb incarnation than the 330 in it's 180gb form. I would probably say at this point, with prices as low as they have fallen from just six months ago, I would only consider the 520 series if shopping for Intel SSD's.
Now, as to your other question about the Samsung or M4. The biggest difference that you are going to see is with the consistency of performance as time marches forward. The feedback I have heard from everyone I know with either of those drives or any SSD based around the Marvell controller is that they do not fall off the edge of the earth in write speed at a certain point, which unfortunately the Intel drives will if you are planning on filling them to near capacity. Their raw, peak sequential benchmarks will be lower in general than Sandforce drives like the Intel, but that isn't really a practical metric of performance. Also, if you are handling lots of uncompressed data (media files, ect)- the Samsung or M4 would make far more sense. They handle all data in the same fashion, whereas the Intel drives do not handle such files as efficiently as compressible data.
I would say there is no way you can go wrong with a Samsung 830/840 drive, or a Plextor M5S drive either (another drive that has similar attributes to the Samsung in behavior). I would probably go for larger than the basic 120gb, as the convenience of not having to concern yourself over things like which drive to place your user library of downloads and documents is wonderful. Now, if there is a great deal on any of the Intel drives and you are really just looking for a giant leap forward from a standard spinning HDD for your operating system, you can't go wrong with any of them. Intel still has a great reputation for reliability, and an OS drive shouldn't really even approach a data volume that would be of concern with the 120gb option. You just would need to be mindful to set your internet browser's DL location and other such items for your primary storage disk.