I like the Garrett for two reasons only, the all metal mode on the GTI 2500 and the sizing which makes it a bit easier then using the pinpoint function to tell size.
OK the big screen is great also.
Depth in discriminate (for both) the Explorer is superior though I guess they are close when true all metal is turned on.
I think they would need to re-balance the 2500 it is harder to swing then the 2500 to my surprise! (aka feels heavier)
Both are fairly easy to use, yet the 2500 discrimination is by far more jumpy and the tones can't be solely relied on to decide to dig or not. That is possible w/ the Explorer.
For relic both are great, though the Explorer has a slight edge when looking for none ferrous relics thanks to the "ferrous tones".
Else they are pretty close.
The Explorer is more sensitive on small targets in discriminate mode then the 2500.
So for coin/jewellery shooting I'd never use a Garrett though for relic it is something to consider I have to say.
But I do prefer my Explorer. My pal likes the 2500 better because it doesn't remind him off Super Mario bros(Nintendo).

He laughs every time he hears my Explorer...
This pretty much tells me what I think of those two, never used the E-Trac though.