I've used TOSSIM for TinyOS and it worked well for me.

Well i think it is better to use MIXIM with OMNET. Simulations would be easy. Also Visual Sense could be easy and then ofcourse Castalia is also good when used with OMNET

You can use any of the following

1. OMNET++ (with INET framework)

2. NS-2

3. OPNET (you need to purchase a license)

All are good simulators, but I personally like OMNET++

Apart, this article may be helpful

https://www.researchgate.net/publication/234018317_A_Performance_Comparison_of_Open_Source_Network_Simulators_for_Wireless_Networks?ev=prf_pub

Conference Paper A Performance Comparison of Open Source Network Simulators f...

I strongly recommend ns2, it very reliable, in other words it is a realistic simulator.

Here is the Survey of Wireless Sensor Network Simulation Tools

http://www.cse.wustl.edu/~jain/cse567-11/ftp/sensor/index.html

We can use any of the following based on parameters

1) language used,

2) userfriendliness,

3) os required,

4) whether simulator is commersial, non-commersial, freeware,etc

Some Commonly used Network Simulators

1. OMNET++ (C++,Open source)

2. NS-2 (using C++ &OTCL,open source)

3. NS-3 (Python& C++, open source)

4. OPNET (C&C++,Commersial)

5. Qualnet (Perl,user-friendly but commertial)

6. Real(C,Commersial)

7) JSIM(Java, Non Commersial)

OMNET+ Opnet + NS 2

I suggest to use NS 2

OMNET++ (with INET framework and Castalia)

Whether NS3 simulation data are being accepted in good journals