Just a thought....
If you wan't to collect all of the Pantaloon Stuff to go for the Big Metal Unit in Throne of Bhaal you will have to use the same Character through all of the Games, and that wouldn't be possible if you play BG2 before BG1...

Spoilers ahead: http://baldursgate.wikia.com/wiki/Golden_Pantaloons

I played the second game back in the day and picked up both EEs a few days ago. Well, I have to say my fears were confirmed in the sense that the first game isn't quite as imaginative as the second. The environments are mainly forest, sometimes a cave or parochial town. The story, at least the first few chapters is a pretty standard ''find out who's behind the bandits'' plot. I'm sure it gets better but I was pretty demotivated coming from BG2, which is amazingly diverse and intriguing right from the get-go. The first game is rather traditional in some ways though well-made, but they really pulled out all the stops for the second. So definitely play them in order.

I played BG2 before BG1 back in the day, at first it was hard to get into BG1 after playing the sequel, which improved a lot of things. But after many years of playing both (especially after the Baldur's Gate Trilogy mod became my standard installation), I see them as a single huge game and enjoy them both equally. :)

Can confirm the "single huge game"... though I played BG1 before BG2 (without Shadows...), and the 1st Big Whoha Experience for me was the EAX Surround(*1) used on BG1 (was the first time I had 4 speakers mounted) and moving in Candlekeep and just hearing the SFX directional was simply overwhelming - not a single person shooter afterwards matched that 3D sound experience I had with BG1.
And just meeting the NPCs 1st in BG1 is on an emotional POV far more better then to have played BG2 before BG1, and BGT adds up to the experience in keeping them consistent throughout the 2 Main games with the expansion for each....

*1: not sure whether it was on my SB128, or on my SB 1st gen. Live!, but as the 128'er was just an Ensoniq under CL label, I would guess it was the Live! (not even sure whether the drivers for the 128'er had incorporated EAX or not).