We use Visual Website Optimizer (VWO) as our primary A/B testing platform of choice as it has an easy to use interface, does not provide extra load on a client's website (it loads async), and has all the basic features to run an effective optimization program. Most importantly, it seems to be the most cost-effective alternative to Optimizely.
A/B test analysis is not great. Instead of giving you a specific number on lift, it gives you a range and calculates "likeliness to beat control". This is due to the fact they use Bayesian statistics and not Frequentist. Though I don't think they need to move away from B Statistics, having a specific numbered lift, like X% better/worse, would be extremely helpful in communicating the effect a test has to clients.
No easy way to see how long a test has been running. Must look at the date range on a different view in analysis and then count the days. Very annoying since it could easily be solved by just listing the duration in days somewhere.
Cannot compare conversion rates over time. Optimizely and most other AB testing platforms create a nice chart that shows how the conversion rates of different variations have changed in relation to each other overtime. VWO does not. Instead it gives you a line chart of the amount of conversions per variation over time. So naturally the line chart just keeps growing because conversions keep coming in. But comparing amount of conversions is very misleading since its conversion rate we care about.
Heatmapping on VWO is one of the best selling points of VWO. Spending time to set up heatmaps in other platforms (including Optimizely) can be tedious and time consuming. Having quick access to these heatmaps that are automatically created saves a lot of time and is very informative when doing post-analysis on a test.
Optimizely is best in class, but extremely expensive. We found Omniconvert and Convert to have some benefits, but fell short on interface and reliability. Adobe Target is possibly the most-expensive and the hardest, most-unpleasant to use and setup, so we'd never recommend it. VWO fits in nicely in having a simple interface, all the key features, very reliable, great support, and a very competitive pricing model.
If a client has a large budget and would like "best in class", Optimizely is hands down the way to go. However, with a smaller budget, VWO in my opinion is the next best option as other platforms fall short.