as now ex-pingdom.com user I though I could share with you my almost 8 months hands-on experience – I’m using uptimerobot.com since 21st July 2014, so I assume the time series is long enough to make an objective opinion.
A lot of checks for free (in comparison with pingdom.com) – 50 monitors and 5 minute check interval, can check by “ping”, TCP connection or by checking for keyword on website. Pingdom allows 1 check and 1 minute interval for free (it used to be like that now it seems the free is gone for good). The paid plans are really expensive with Pingdom – like 15 USD to check 10 websites with 1 minute interval, that’s really insane…
The uptimerobot.com offers for 4.5 USD/month 50 checks with 1 minute interval and 20 SMS – it’s really a no brainer…
The Not so Awesome:
User interface is really not the best and there is a lot of space for improvement but the price and features are really unbeatable – in any case the most important is the message you receive on your email and that is absolutely clear.
Pingdom.com really doesn’t make any sense to me, I don’t see any advantage to pay more for same service – their plan for checking 50 websites with 1 minute interval costs like 45 USD/month (!!!) which is outright insane. Btw. I also contacted support on uptimerobot.com few times (using free account) and received reply within few hours, really awesome! I also tried pingscope.com but I was not particularly impressed – UI seemed really old and if I remember correctly there were some features missing.
I’ve no affiliation with uptimerobot.com (as you can see no referral links). I just thought I should share my positive experience with alternative service for fraction of the price.