i have had both phones, the optimus, and wildfire are both great phones, i like the wildfire because of the sense ui, i dont really like the "vanilla" look of 2.2 froyo. the wildfire has a 5 mp cam and flash, the optimus has a 3.2mp cam no flash. there both pretty fast when there clean, the one flaw with the wildfire is the lack of memory, you can get around that by rooting, and maybe installing a custom rom...
gps seems faster on the wildfire, but could be where i am..