best solution to conect a Private LAN to the internet ?

hi, we have a Private LAN with over 140 PCs.

we recently decide to connect all PCs to the internet . what is the best solution tosecurely connect our clients to internet  ?

1- using Microsoft proxy base solutions like TMG ?

2- using 3rd party UTM solutions ?

3- using NAT server placed in DMZ ?

4- using secondary DNS server placed in DMZ with forwarders ?