I prefer Gmail as it is clean and clear. 

I am tired of the hierachial view as it looks messy and too busy on the eyes. 

If Zoho can offer you the choice then they are onto a winner..

This was my biggest pet peeve with GMail. It was a mess the way they handled conversations. I could never which was the latest piece as new conversations keep getting appended. As good as GMail can be, I could not use it for work because of this alone.

Well i think both of them have their goods and bads but both of them start looking ugly when a thread goes long..

Now i am just waiting for IMAP support so that i can access my gmail account from zoho using IMAP, pop3 is ok but not good as IMAP..

It depends. The hierarchical makes it easy to see the structure, but other email apps (thunderbird) offer similar info but it makes it difficult to find new messages because they are all spread out. I like to have my new email together.

Come on Guys. What is this!

I am seeing threaded views since my abc days on keyboards - late ninties. So where is your innovation on it? Conversational views is good for small screen. I guess iPhone can be considered to be a pioneer. Touch sreen base collapse and expands. Here conversational view is a perfect fit. 

Threded view is good for laptops or desktops. 

But then what the heck? Where is your out of the box thinking??? There can be many ways a mail can be shown!

Love the hierarchical view. It adds so much information to the view. It's not a clean, that's ok, it's not suppose to be clean it is suppose to convey meaning. Other view are available for a cleaner view. Gmail non hier. view has always been a turn off for me. Go Zoho Mail!

For personal use, I prefer GMail's interface--conversations are rarely as structured as the hierarchical view suggests, and the stack of cards interface allows you to have the full body of a number of e-mails on screen at the same time, which is particularly sensible when you've got a series of rapid one-line e-mails. It also reduces the number of entries needed in the inbox view (one per thread, rather than one per message).

I can see the advantage of the hierarchical view, but for what I use it for, I prefer Google's concept.

I prefer gmail because I feel more organized when using it.  The hierarchy view seems pretty Web 1.0.  Giving a user the choice between the two options is a great way to go.  Still, I wonder if there's a way to sort email that hasn't been used yet and is worth exploring.

I also prefer Gmail's interface. But the key is not the conversational vs. threaded view. It's the hiding of emails' subjects. Gmail goes straight to the added comment and shows it next to speaker's name. Their stack of cards is not obfuscated by the repeated subject line accompanied with all the "Re: [Fwd: Re:] RE: Fw:" stuff. In your Zoho screenshot the most part of the screen is taken by the subject lines that don't bring anything to the conversation.

gmail conversation view looks neater/simpler. it could be improved by a  toggle between compressed view (stacked) and  expanding all emails in the stack (maybe zoho can do this; currently gmail seems to have a default behavior of keeping all clicked emails expanded which doesnt seem to be that useful). Agree with Jorek that most importantly gmail avoids repetition of subject..  maybe that is the key..  putting snippets in the header and see how that impacts usability. the problem with the visual hierarchy is that it wastes screen real estate by indenting and doesn't add much value.  if there is a way to represent the thread structure without indenting  then each each row in the stack has the same space for snippets and the stack will also look  consistent/neat as elements are aligned across rows.  

gmail's buttons are ugly and hard to use (star is an exception); zoho wins in overall UI design.  the other key difference is that gmail blurs the distinction between the list of emails and the content of the email (no split panes); this can be efficient for some people but may confuse others (just like labels vs folders)

I prefer Zoho's view, but the hierarchy is distracting.  Frankly, I prefer Apple Mail threading behavior:

1) All messages in a thread can be grouped (similar to gmail but takes even less vertical space)
2) All messages in a thread can be expanded, but there is no distracting hierarchy.  I can see each respondent's name and subject (name is more important)

I use gmail as a service which is awesome, but I despise their web UI.  It's nearly unusable.  Watch a non-techie user try to use it and you will be shocked.  

Now, don't get me started on using email as a 'productivity tool' for work.  Yech.  Who wants to wade through email threads?  Consumer-oriented wikis or message forums, eg Basecamp, are far superior.  And this is coming from an old guy, 40+

Thanks for the comparison screenshots.

I'm going for the Zoho mail - the interface is clean, the threads with the beginning of the message are great, and to be honest, I just don't get the no folders etc of GMail - shoot me if you like, but at least Zoho gives me the choice......

Gmail view is better and clean to access.

The conversations can be expanded or contracted as required and all the threading is maintained manageably.
Zohomail has to do better on the UI.

>>> the problem with the visual hierarchy is that it wastes screen real estate by indenting and doesn't add much value.  if there is a way to represent the thread structure without indenting  then each each row in the stack has the same space for snippets and the stack will also look  consistent/neat as elements are aligned across rows. 

colors ;) coloring separate threads.