Looking for advice, thoughts from anyone who has tried either -- $30 is a lot to drop on an iPhone dictionary and I'd like to make sure I pick the right one.

Here's my preliminary thoughts, obviously offered without trying either:
Both are priced within $5 of each other so no difference there. Both are considered to be very thorough dictionaries so probably a draw or slight edge to the AH based on reviews of the hardcover versions on Amazon.

American Heritage:
Pros: color pictures, maps, diagrams, etc.; exact copy of the hardcover edition for your phone; like the idea of a standalone app; good reviews on iTunes (other than the usual price complaints); real time progressive lookup so starts to find words as you type them;
Cons: 300+ mgb file size!

Meriam Webster Collegiate 11th Ed. through eReader.com.
Pros: file size is 11mb.
Cons: No reviews or thorough description on eReader site so can't tell what this one has to offer beyond basic dictionary fare in b&w text and how well it functions on iPhone; don't know if this one has real time progressive lookup which is a key function especially if you are spelling a word wrong but close;

Appreciate hearing from anyone who has purchased or used either of these.

Thanks!