About a year ago I conducted a thorough analysis of multiple marketing automation platforms. This included: Eloqua, Marketo, HubSpot, InfusionSoft, Pardot, SalesFusion and a few others. Eloqua (acquired by Oracle) is in a class by itself but it's a very complex and costly platform. In the end it came down to Marketo vs. HubSpot. I ended up going with HubSpot. It had a much easier to use, more intuitive interface and some really good SEO features and an integrated blog platform. The price of both products was comparable ($1300/month for 10K database I believe).
One of the products I looked at which was interesting was InfusionSoft. It's in the lower end of the product spectrum...an entry-level MA system but it was pretty decent for the price. Plus, it comes with integrated CRM. Keep in mind that with most MA platforms, you need to factor in the cost of your CRM licence. The company I am currently investing in is using InfusionSoft and it's working very well for them. Consider this type of product as "marketing automation training wheels".
One thing I learned is that you really need to setup your MA system properly and fine tune it over time for it to yield results. This includes mapping out your inbound processes, developing your content plan, setting up your lead conversion forms, autoresponders, building your nurturing tracks, etc... You can buy Eloqua but if you don't set it up properly, you're wasting money. Most MA vendors will assign a success team to your account to make sure you get off the ground smoothly and quickly. This is often part of the start-up fee they charge. The HubSpot team was great.
One thing for sure is that marketing automation is no longer a nice to have. It's mandatory! These systems, if put to proper use, can be incredibly powerful and effective for driving inbound leads and converting leads into customers. I can't see how any company can operate without one.