Best is a relative term. IMO for Macs, the Crucial M4 is my top personal pick. This is because the ratings on the M4 are as good as any SSD on the market and Crucial as a company delivers when a firmware update is required. History has shown that other companies have dragged their feet (and even denied a problem exists) where as Crucial knew a problem existed and in a matter of weeks fixed it outright. Quality-wise, my Crucials kick ass. If you do not plan to run TRIM, the Crucial M4 may actually be the best pick of the SSDs due to its controller. And Crucial also gives excellent support for us Mac people. I cannot say enough good things about them as a company, and the thousands of other Crucial SSD owners say the same thing (heck, look at the reviews in the link!).
Now, the Samsung 830? Also, absolutely, positively spectacular. Samsung doesn't get enough credit when we all talk SSDs. They have proven with the 470 and others that they get the job done, are extremely reliable, and run at the speeds they promise. Their customer service is also very well-rated. The reliability record of the 470 is as good as any and so there is no reason to not expect the same upstanding reliability record with the 830.
Actual speed differences between the two? In real life usage, both are going to be fast with all types of data. The M4 often looks poorer on paper than it is, and many tests show the older firmware revisions which had lower speeds. The actual world performance of my M4s are as good as anything else I have or better.
So which one is better? No one is going to be able to tell you that. I would say see if you can get one much cheaper than the other, as this really is a win-win. If you are going for a Mac without using TRIM, I would read up on the Marvell controller used in the Crucial as it seems that the Marvell controlled SSDs give the best overall performance in non-TRIM-enabled OS environments. Again, I would read up on it to make your own decision as some conflicting info exists. Either one will provide some of the best performance hands down with amazing reliability. The feedback on them shows just how well-made they are and you really can't go wrong.