If you are looking to do cold-email blasts to prospects a traditional provider like sales-push, mailchimp, or responsys is not going to get great click-through or response rates because people instinctively tune out and unsubscribe because it's spam.
A series of plain-text emails will be the best for this. Outreach.io ($100 / mo) or Yet Another Mail-merge (free Google Sheets plug-in) will be the best. Outreach.io is great because you can create email sequences and so much more, however.
I don't have all the details with regards to what you are looking to accomplish so it's hard to say. However, if you are getting people signing up for a list (via blog, paid ads, etc) then a mail list provider with marketing automation included is ideal. For starting out, most startups use Mailchimp because it's easy to set-up, has strong analytics, and includes Mailchimp automation (marketing automation) and Mandrill (transactional emails / basically competitor to Sendgrid).

Tools to use if you need mail-list / marketing automation:
High End
-responsys - most expensive but best
-epsilon
-exact target
-experian

Mid-tier
-Silver pop
-strong mail
-lyrics
-sail thru

SMB/Startup
-mailchimp - most startups use this to start and then switch later once it becomes less cost efficient
-vertical response
-icontact
-campaign monitor