After nearly 2 years 20i seem really pretty good
I've been with 20i close on 2 years now after slowly migrating from Heart. The admin area is clean and easy to use, support is fast, helpful and kind(!), i've had very little downtime (looking at you heart!) and actually i can't remember any down time.
And they're cheaper.
before heart i have tried, easyspace, ednet/lumison/Polsant, fasthosts, 123Reg and have other clients on Godaddy, Names, 1and1 and others.
For shared and reseller hosting i think 20i might be the best.