Standard hand with top pair, facing pot-sized bet on the river

[fabadam]

This was the hand that had me thinking the longest tonight.
I am open to comments on earlier streets, but am mostly interested in the river. What is your action if:
(1) villain is unknown.
(2) villain is rather loose, but not very aggressive so far
(3) villain seems a bit LAG, and specifically has AF by street of 2.0/1.5/6.0.

Image of hero is TAG/LAG, I have been playing 22/20/10 on this table so far, with lots of automatic c-bets on the flop, not showing down a lot at all.

Everest Poker No-Limit Hold'em, $0.25/$0.50 (HH Converter by Kreatief)

Button (48.00)
SB (50.30)
BB (97.95)
MP3 (57.90) (Hero)
CO (46.50)

Preflop: Hero is MP3 with Q[img]/images/graemlins/spade.gif[/img], J[img]/images/graemlins/diamond.gif[/img]
<font color="#CC3333">Hero raises to $2.00</font>, <font color="#666666">2 folds</font>, SB calls $1.75, BB calls $1.50,

Flop: J[img]/images/graemlins/spade.gif[/img], 5[img]/images/graemlins/diamond.gif[/img], 3[img]/images/graemlins/club.gif[/img] ( $6 )
SB checks, BB checks, <font color="#CC3333">Hero bets $6.00</font>, <font color="#666666">1 folds</font>, BB calls $6.00,

Turn: 6[img]/images/graemlins/club.gif[/img] ( $18 )
BB checks, Hero checks,

River: A[img]/images/graemlins/heart.gif[/img] ( $18 )
<font color="#CC3333">BB bets $18.00</font>, Hero ???,