Hi there idig2.
I've had a GTI 1500 and a safari. The 2500 is very similar to the 1500.
Here are the differences including my bias.
Coil - The safari has a DD coil, whereas the GTI has a cocentric. The DD coils are better in mineralized ground, separate better, and have largely consistent depth along the length of the coil. A large DD coil is still quite good in trashy ground, while a cocentric suffers more from masking. Cocentrics can be easier to pinpoint with if you have grown up with them. You will see that many of the high end detectors now have DD coils (V3, etrac) and now the ATpro. You can buy DD coils for a GTI, but you loose imaging.
Imaging - this is a sizing function specific to the GTI series and is a really nice ID tool. For example a nickel and pull tab may have the same signal but a pull tab will most commonly have a size C - a nickel will have size B. This theoretically could be very helpful in hunting for gold, where many small items will be size A or B, and pull tabs size C. The imaging function works effectively up to 5 inches or so.
Weight - they are both beasts.
ID and disc. Both have notch descrimination, but safari's numerical ID readout goes from -10 to +40, whereas the GTI goes from 0-12 in 0.5 increments. I find that the safari is much better in the middle conductivity range - nickels, gold, pull tabs, up to zinc and indians than the GTI, but that the GTI is better at differentiating between a copper penny, dime, quarter and half dollar.
Sunray probes - you can get a Sunray probe for either, and both work well.
Frequency - the safari has multiple simultaneous frequencies - so it is great with wet sand, EMI and so forth. The GTI runs on a single frequence that can be slightly changed for competition hunts and this sometimes helps with EMI, but I often had problems with the GTI where it would freak out, and I would have to turn the sensitivity way down.
Irritating qualities - the safari can be noisy as all get out if you have the sensitivity too high and have trashy ground. On the other hand it can run really quietly if you have it set more modestly.
Depth and finds - I found deeper stuff with the safari and more silver/wheats/V-nickels/buffalos, but never have done a side by side test, so I cannot say for sure that the safari is deeper.
Customer service - the customer service of Garrett is known to be good, whereas Minelab's has a terrible reputation. That said, both are very solidly built, and I have had no problems with either.
In any event, both are great coin machines. Given the choice again, I'd go for the safari, but the GTI is easy to use and a bit cheaper and not a bad choice. Between the 1500 and the 2500 - I'd go for the 1500 unless you want to add on one of those super deep cache hunting set-ups.
