InnoDB and MyISAM each have their strengths and weaknesses.

• May 03, 2012 : Which is faster, InnoDB or MyISAM?
• Sep 20, 2011 : Best of MyISAM and InnoDB

If you have enough RAM, I would choose InnoDB because it caches data and index pages in the Buffer Pool. MyISAM only caches index pages in the Key Cache.

MyISAM tables experience full table locks for each INSERT, UPDATE, and DELETE. MyISAM tables always require disk access for data.

InnoDB tables always incur disk I/O in the following areas:

• Double Write Buffer : Changes are posted in ibdata1 to avoid OS caching
• Insert Buffer : Changes to Secondary (non-Unique) Indexes as posted in ibdata1
• Data and Indexes
  • With innodb_file_per_table = 0, changes are written to ibdata1
  • With innodb_file_per_table = 1, changes are written to .ibd tablespace file. Read I/O against ibdata1 still necessary to crosscheck table metadata

SUMMARY

In an environment with the following:

• heavy writes
• heavy reads
• tons of RAM
• heavy connections

I would always choose InnoDB. Please check out my other post about InnoDB over MyISAM : When to switch from MyISAM to InnoDB?

When would I every choose MyISAM?

Under the following scenario

• Using MySQL Replication
• Master with all InnoDB
• Slave with all tables converted to MyISAM
• ALTER TABLE ... ROW_FORMAT=Fixed for all tables on the Slave

Disk I/O wise, MyISAM has a slight edge with ROW_FORMAT-Fixed because you only interact with one file, the .MYD file. The row size is completely predictable because VARCHAR is treated as CHAR this shortening access time for data retrieval.

• May 10, 2011 : What is the performance impact of using CHAR vs VARCHAR on a fixed-size field?
• Mar 25, 2011 : Performance implications of MySQL VARCHAR sizes

On the other hand, InnoDB has to interact with multiple files (ibdata1, serveral read/write threads upon the .ibd of the InnoDB table).

You could merge overlapping intervals and count the hours from there (untested):

select name, min(start), end 
from (
    select x.name, x.start, min(y.end) as end 
    from t as x 
    join t as y 
        on x.name = y.name 
       and x.start <= y.end 
       and not exists (
           select 1 
           from t as z 
           where y.name = z.name 
             and y.end >= z.start 
             and y.end < z.end
       ) 
    where not exists (
        select 1 
        from t as u 
        where x.name = u.name 
          and x.start > u.start 
          and x.start <= u.start
    ) 
    group by x.name, x.start
) as v group by name, end;