Tough call. I think Graham isnt far from Bryant as far as numbers go, and that is coming from a TE.
I actually like both offers and think both are a decent play for Bryant. Your WR takes a bit of a hit here but you get a massive upgrade at TE, which I find is a harder position to fill for numbers.
I actually like Garcon better then Nicks and Decker (the other prime WR on your current roster) as he is RGIII's primary target. Of course, thats when both Garcon and RGIII are on the field at the same time (which only happened for 9 games last year). Thats my concern for him though, his health. Apparently he is healthy, for now, but I dont have a lot of faith in him staying that way.
Tavon Austin hasn't had a great pre-season (his 2nd game was better then his 1st) so far but you have to think he will be the prime target long term for the Rams.
If you think your team has a shot to win this year, I'd probably take it with Garcon and hope he can stay healthy, but thats just me.