There are huge differences in speeds and numbers of program/erase (PE) cycles between CF cards. Speeds are well covered lots of different places, PE cycles tend to vary between 10,000 for the lower end cards to more than 1million at the high end. Check the rating of the specific card you're looking at.
Both SSD and to some extent CF manufacturers seem to avoid mentioning PE cycles directly, advertising an MTBF number instead. This is kind of understandable because the SSD/CF present a block level interface to the controller, with the card/drive managing the mapping of logical block to NAND cell, with wear leveling thrown in the middle. So you don't necessarily know how many NAND cells there are (there may be significantly more than the capacity presented to the controller, which will be used for wear leveling) which makes it a little difficult to extract meaning from a PE cycle count. Then there's MLC vs. SLC in SSD, with SLC having significantly more write cycles, and MLC having comparable write cycles to most CF cards.
In addition to all that, the wear leveling implementation can make a noticeable difference in usability as well. For example, with the cheaper (I particularly notice it with 133x and lower) CF cards will get reasonably decent write performance for a little while, then slow to a crawl as wear leveling kicks in, then jumps back up. On the other hand, higher end CF and nearly all SSDs don't have this problem (or at least isn't nearly as noticeable).
But, all this should be weighed against how it is being used. 100,000 write cycles in a 133x CF card might be pretty slow and seem short lived, but if you're putting it into a machine with a 5MB/s SCSI interface that you'll turn on once every 6 months, does it really matter?
Personally, I've been using SanDisk Ultra cards (plain old Ultra) and it has been fine for my uses. Most recommendations I've read seem to recommend Ultra II at a minimum and the Extreme cards are preferred. Those are much better cards, and I'd recommend them as well.
As for VM, there's nothing special about it from the card's perspective. It's just yet another IO operation. I do not know enough about the specific implementations of the various versions of Mac OS VM to be able to intelligently comment on how they would interact with CF vs. SSD.
Anyway, those are just my experiences and observations FWIW. If you read the numerous other posts here on the subject, there are a lot of people with different experiences and observations.
Both SSD and to some extent CF manufacturers seem to avoid mentioning PE cycles directly, advertising an MTBF number instead. This is kind of understandable because the SSD/CF present a block level interface to the controller, with the card/drive managing the mapping of logical block to NAND cell, with wear leveling thrown in the middle. So you don't necessarily know how many NAND cells there are (there may be significantly more than the capacity presented to the controller, which will be used for wear leveling) which makes it a little difficult to extract meaning from a PE cycle count. Then there's MLC vs. SLC in SSD, with SLC having significantly more write cycles, and MLC having comparable write cycles to most CF cards.
In addition to all that, the wear leveling implementation can make a noticeable difference in usability as well. For example, with the cheaper (I particularly notice it with 133x and lower) CF cards will get reasonably decent write performance for a little while, then slow to a crawl as wear leveling kicks in, then jumps back up. On the other hand, higher end CF and nearly all SSDs don't have this problem (or at least isn't nearly as noticeable).
But, all this should be weighed against how it is being used. 100,000 write cycles in a 133x CF card might be pretty slow and seem short lived, but if you're putting it into a machine with a 5MB/s SCSI interface that you'll turn on once every 6 months, does it really matter?
Personally, I've been using SanDisk Ultra cards (plain old Ultra) and it has been fine for my uses. Most recommendations I've read seem to recommend Ultra II at a minimum and the Extreme cards are preferred. Those are much better cards, and I'd recommend them as well.
As for VM, there's nothing special about it from the card's perspective. It's just yet another IO operation. I do not know enough about the specific implementations of the various versions of Mac OS VM to be able to intelligently comment on how they would interact with CF vs. SSD.
Anyway, those are just my experiences and observations FWIW. If you read the numerous other posts here on the subject, there are a lot of people with different experiences and observations.