Both Propecia and Rogaine can "regrow" some hair. Just look at the Propecia.com website to see photos of visible regrowth from the clinical trials. However, the consensus is that Rogaine regrows more hair, over the short term. Bryan posted this summary of results a while ago:
The Glaxo trial of finasteride and dutasteride
Finasteride... +72 hairs, six months (12.0 hairs/month)
Dutasteride... +108 hairs, six months (18.0 hairs/month)
Various topical minoxidil studies
(1) 2% minoxidil... +425 hairs, 12 months (35.4 hairs/month)
Also: 3% minoxidil... +372 hairs, 12 months (31.0 hairs/month)
(2) 2% minoxidil... +273.4 NONVELLUS hairs, 12 months (22.8 hairs/month)
(3) 2% minoxidil... +101 TERMINAL hairs, 13 months (7.8 terminal hairs/month)
(4) 1% minoxidil... +149 hairs, 6 months (24.8 hairs/month)
Also: 2% minoxidil... +175 hairs, 6 months (29.2 hairs/month)
(5) 2% minoxidil... +233.8 hairs, 12 months (19.5 hairs/month)
(6) 2% minoxidil... +151 hairs, 4 months (37.8 hairs/month)
Also: 2% minoxidil... +324 hairs, 12 months (27 hairs/month)
Also: 3% minoxidil... +166 hairs, 4 months (41.5 hairs/month)
Also: 3% minoxidil... +338 hairs, 12 months (28.2 hairs/month)
The Glaxo trial of finasteride and dutasteride
Finasteride... +72 hairs, six months (12.0 hairs/month)
Dutasteride... +108 hairs, six months (18.0 hairs/month)
Various topical minoxidil studies
(1) 2% minoxidil... +425 hairs, 12 months (35.4 hairs/month)
Also: 3% minoxidil... +372 hairs, 12 months (31.0 hairs/month)
(2) 2% minoxidil... +273.4 NONVELLUS hairs, 12 months (22.8 hairs/month)
(3) 2% minoxidil... +101 TERMINAL hairs, 13 months (7.8 terminal hairs/month)
(4) 1% minoxidil... +149 hairs, 6 months (24.8 hairs/month)
Also: 2% minoxidil... +175 hairs, 6 months (29.2 hairs/month)
(5) 2% minoxidil... +233.8 hairs, 12 months (19.5 hairs/month)
(6) 2% minoxidil... +151 hairs, 4 months (37.8 hairs/month)
Also: 2% minoxidil... +324 hairs, 12 months (27 hairs/month)
Also: 3% minoxidil... +166 hairs, 4 months (41.5 hairs/month)
Also: 3% minoxidil... +338 hairs, 12 months (28.2 hairs/month)