What is the best and most performant MySQL cloud solution?
I'd like to chime in on what has been said in the question and in the comments.

XEROUND

Exactly one year ago today, I wrote an answer about the Xeround DB Service : Database as a service (DbaaS) over dimensions--performance, scalability, &amp; reliability?

Granted, you have the following:


Ability to create a Cloud Database and immediately put data into it without any strings attached
Access to a Whitepaper on the Xeround Storage Engine (Overview) from Feb 2012
There is a good FAQ section provided
There is an API for it


I just instantiated a Xeround Free Version Sevice and ran SHOW ENGINES; and got this

mysql&gt; show variables like '%innodb%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| have_innodb           | NO    |
| ignore_builtin_innodb | OFF   |
+-----------------------+-------+
2 rows in set (0.01 sec)

mysql&gt; show engines;
+---------+---------+-----------------------------------------------------------+--------------+------+------------+
| Engine  | Support | Comment                                                   | Transactions | XA   | Savepoints |
+---------+---------+-----------------------------------------------------------+--------------+------+------------+
| Xeround | DEFAULT | Xeround MySQL storage engine                              | YES          | NO   | NO         |
| MyISAM  | YES     | Default engine as of MySQL 3.23 with great performance    | NO           | NO   | NO         |
| MEMORY  | YES     | Hash based, stored in memory, useful for temporary tables | NO           | NO   | NO         |
+---------+---------+-----------------------------------------------------------+--------------+------+------------+
3 rows in set (0.01 sec)

mysql&gt;


No InnoDB ??? Not much has changed.

How about variables for the Storage Engine?

mysql&gt; show variables like 'xeround%';
+------------------------------------+-------------------------------------------+
| Variable_name                      | Value                                     |
+------------------------------------+-------------------------------------------+
| xeround_alloc_pages                | 1                                         |
| xeround_alloc_stats                | 0                                         |
| xeround_conditional_filtering      | off                                       |
| xeround_conf_dir                   | etc                                       |
| xeround_database_schema_size_limit | 2                                         |
| xeround_database_size_limit        | 10                                        |
| xeround_enable_client_socket_check | ON                                        |
| xeround_index_stat_is_approximate  | ON                                        |
| xeround_instance_id                | 35644                                     |
| xeround_maintenance_mode           | OFF                                       |
| xeround_query_row_cache            | 0                                         |
| xeround_record_count_adjust        | 12                                        |
| xeround_records_in_range_mode      | off                                       |
| xeround_schema_id                  | 115                                       |
| xeround_throughput_credit          | 100                                       |
| xeround_throughput_credit_seconds  | 10                                        |
| xeround_transaction_memory_limit   | 128                                       |
| xeround_transactional_ddl          | OFF                                       |
| xeround_xdapc_ip                   |                                           |
| xeround_xdapc_socket               | /opt/xeround/sys_35412/xdapc/xdapc_socket |
+------------------------------------+-------------------------------------------+
20 rows in set (0.01 sec)

mysql&gt;


Looking at the API, I do not believe you can tune anything. You are basically at the mercy of the Storage Engine.

I have also tried loading data into it and using the INFORMATION_SCHEMA database to report back to me space usage. For the XEROUND Storage Engine, I get back nothing. MyISAM is OK.

There are still other limitations with Xeround (Oct 12, 2012) you have to read and consider.

Amazon RDS

While the service bears the hallmarks of a well-trusted brand name, the service must still be evaluated in terms of two things:


Cost
Configuration 
Performance


While cost is at one's discretion, I will discuss the other aspects

CONFIGURATION


You have no access to a my.cnf
Any variables to be configured beyond default requires an API call to the DB Parameters Group followed by a restart of the RDS Instance.
There are two things you cannot change no matter what Memory Class you choose


max_connections
innodb_log_file_size

See my post from Aug 02, 2012 : Local database vs Amazon RDS


PERFORMANCE

This goes hand-in-hand with CONFIGURATION. Any tuning aspects you wish to make are subject to the limitations and functionality of the RDS API. Not all Performance enhancements for InnoDB are possible because of Amazon's policies meant to provide a share-everything environment for normal RDS users (unless you can come up with more $$$ for more IOPs and things of this nature).

EPILOGUE

Amazon EC2 may be your best option if your want more flexibility/autonomy for


configuring MySQL
voluntarily paying


RAM
Disk
IOPs

tuning InnoDB


Given the times you just reported in the question, nothing short of due diligence is required for tuning (possibly rearchitecting) your app for Cloud Usage.